import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.NoSuchElementException;
import java.util.concurrent.SynchronousQueue;
public class Main implements Runnable {
public static void main(String[] args) {
// long t = System.currentTimeMillis();
new Thread(null, new Main(), "", Runtime.getRuntime().maxMemory()).start();
// System.err.println(System.currentTimeMillis() - t);
}
String min(String a, String b) {
if (a.compareTo(b) <= 0) {
return a;
} else {
return b;
}
}
String concat(String a, String b) {
return min(a + b, b + a);
}
class DJSet {
int n;
int[] upper;
public DJSet(int n_) {
n = n_;
upper = new int[n_];
Arrays.fill(upper, -1);
}
int root(int x) {
return upper[x] < 0 ? x : (upper[x] = root(upper[x]));
}
boolean equiv(int x, int y) {
return root(x) == root(y);
}
void setUnion(int x, int y) {
x = root(x);
y = root(y);
if (x == y)
return;
if (upper[x] < upper[y]) {
x ^= y;
y ^= x;
x ^= y;
}
upper[y] += upper[x];
upper[x] = y;
}
}
int[] col;
int color;
int[] ord;
int order;
int[] low;
ArrayDeque<Integer> pnd;
void scc(ArrayList<Integer>[] g) {
int n = g.length;
color = 0;
order = 0;
col = new int[n];
ord = new int[n];
low = new int[n];
Arrays.fill(col, -1);
Arrays.fill(ord, -1);
pnd = new ArrayDeque<>();
for (int i = 0; i < n; ++i) {
if (col[i] != -1) {
continue;
}
scc_dfs(g, i, -1);
}
}
void scc_dfs(ArrayList<Integer>[] g, int cur, int par) {
ord[cur] = order;
low[cur] = ord[cur];
++order;
pnd.addLast(cur);
for (int dst : g[cur]) {
if (col[dst] != -1)
continue;
if (ord[dst] == -1) {
scc_dfs(g, dst, cur);
}
low[cur] = Math.min(low[cur], low[dst]);
}
if (ord[cur] == low[cur]) {
int v = -1;
while (v != cur) {
v = pnd.pollLast();
col[v] = color;
}
++color;
}
}
int[] sort_ord;
int[] sort_ref;
int sort_order;
void sort_dfs(int cur, ArrayList<Integer>[] g) {
for (int dst : g[cur]) {
if (sort_ord[dst] == -1) {
sort_dfs(dst, g);
}
}
sort_ord[cur] = sort_order++;
sort_ref[sort_ord[cur]] = cur;
}
void sort(ArrayList<Integer>[] g) {
int n = g.length;
sort_ord = new int[n];
sort_ref = new int[n];
Arrays.fill(sort_ord, -1);
sort_order = 0;
for (int i = 0; i < g.length; ++i) {
if (sort_ord[i] == -1) {
sort_dfs(i, g);
}
}
}
String f(ArrayList<Integer>[] g, ArrayList<String> c, int k) {
int n = g.length;
scc(g);
ArrayList<String>[] ss = new ArrayList[color];
for (int i = 0; i < ss.length; ++i) {
ss[i] = new ArrayList<>();
}
for (int i = 0; i < n; ++i) {
ss[col[i]].add(c.get(i));
}
for (int i = 0; i < color; ++i)
Collections.sort(ss[i]);
ArrayList<Integer>[] g2 = new ArrayList[color];
for (int i = 0; i < g2.length; ++i) {
g2[i] = new ArrayList<>();
}
for (int i = 0; i < g.length; ++i) {
for (int v : g[i]) {
if (col[i] == col[v])
continue;
g2[col[i]].add(col[v]);
}
}
sort(g2);
String[][] cur = new String[color][k + 1];
for (int i = 0; i < color; ++i) {
for (int j = 0; j <= k; ++j) {
cur[i][j] = "{";
}
cur[i][0] = "";
}
String[] ss2 = new String[color];
for (int i = 0; i < color; ++i) {
String s = "";
for (String u : ss[i]) {
s += u;
}
ss2[i] = s;
}
String[][] ret = new String[color][k + 1];
for (int i = 0; i < ret.length; ++i) {
for (int j = 0; j < ret[i].length; ++j) {
ret[i][j] = "{";
}
ret[i][0] = "";
}
for (int i = 0; i < color; ++i) {
String[] pre = new String[k + 1];
for (int j = 0; j <= k; ++j)
pre[j] = "{";
pre[0] = "";
for (int dst : g2[sort_ord[i]]) {
for (int j = 0; j <= k; ++j) {
pre[j] = min(pre[j], ret[dst][j]);
}
}
for (int j = 0; j <= ss2[sort_ord[i]].length(); ++j) {
for (int l = 0; j + l <= k; ++l) {
if (pre[l].equals("{") || ss2[sort_ord[i]].equals("{"))
continue;
ret[sort_ord[i]][j + l] = min(ret[sort_ord[i]][j + l], ss2[sort_ord[i]].substring(0, j) + pre[l]);
}
}
}
String res = "{";
for (int i = 0; i < color; ++i) {
res = min(res, ret[i][k]);
}
return res;
}
String solve(int n, int m, int k, char[] c, int[] a, int[] b) {
DJSet ds = new DJSet(n);
for (int i = 0; i < m; ++i) {
ds.setUnion(a[i], b[i]);
}
@SuppressWarnings("unchecked")
ArrayList<Integer>[] vv = new ArrayList[n];
ArrayList<Integer>[][] gg = new ArrayList[n][];
ArrayList<String>[] cc = new ArrayList[n];
for (int i = 0; i < n; ++i) {
vv[i] = new ArrayList<>();
cc[i] = new ArrayList<>();
}
for (int i = 0; i < n; ++i) {
vv[ds.root(i)].add(i);
}
for (int i = 0; i < n; ++i) {
Collections.sort(vv[i]);
for (int v : vv[i]) {
cc[i].add(c[v] + "");
}
}
int[] id = new int[n];
for (int i = 0; i < n; ++i) {
int r = ds.root(i);
id[i] = Collections.binarySearch(vv[r], i);
}
boolean[] vis = new boolean[n];
for (int i = 0; i < n; ++i) {
int r = ds.root(i);
if (vis[r])
continue;
vis[r] = true;
gg[r] = new ArrayList[vv[r].size()];
for (int j = 0; j < gg[r].length; ++j)
gg[r][j] = new ArrayList<>();
}
for (int i = 0; i < m; ++i) {
int r = ds.root(a[i]);
gg[r][id[a[i]]].add(id[b[i]]);
}
String ret = "{";
for (int i = 0; i < n; ++i) {
if (gg[i] == null)
continue;
ret = min(ret, f(gg[i], cc[i], k));
}
if (ret.equals("{")) {
return "-1";
} else {
return ret;
}
}
public void run() {
Scanner sc = new Scanner();
int n = sc.nextInt();
int m = sc.nextInt();
int k = sc.nextInt();
char[] c = new char[n];
for (int i = 0; i < n; ++i) {
c[i] = sc.next().toCharArray()[0];
}
int[] a = new int[m];
int[] b = new int[m];
for (int i = 0; i < m; ++i) {
a[i] = sc.nextInt();
b[i] = sc.nextInt();
--a[i];
--b[i];
}
System.out.println(solve(n, m, k, c, a, b));
}
static void tr(Object... objects) {
System.out.println(Arrays.deepToString(objects));
}
class Scanner {
private final InputStream in = System.in;
private final byte[] buffer = new byte[1024];
private int ptr = 0;
private int buflen = 0;
private boolean hasNextByte() {
if (ptr < buflen) {
return true;
} else {
ptr = 0;
try {
buflen = in.read(buffer);
} catch (IOException e) {
e.printStackTrace();
}
if (buflen <= 0) {
return false;
}
}
return true;
}
private int readByte() {
if (hasNextByte())
return buffer[ptr++];
else
return -1;
}
private boolean isPrintableChar(int c) {
return 33 <= c && c <= 126;
}
private void skipUnprintable() {
while (hasNextByte() && !isPrintableChar(buffer[ptr]))
ptr++;
}
public boolean hasNext() {
skipUnprintable();
return hasNextByte();
}
public String next() {
if (!hasNext())
throw new NoSuchElementException();
StringBuilder sb = new StringBuilder();
int b = readByte();
while (isPrintableChar(b)) {
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
public int nextInt() {
if (!hasNext())
throw new NoSuchElementException();
int n = 0;
boolean minus = false;
int b = readByte();
if (b == '-') {
minus = true;
b = readByte();
}
if (b < '0' || '9' < b) {
throw new NumberFormatException();
}
while (true) {
if ('0' <= b && b <= '9') {
n *= 10;
n += b - '0';
} else if (b == -1 || !isPrintableChar(b)) {
return minus ? -n : n;
} else {
throw new NumberFormatException();
}
b = readByte();
}
}
public long nextLong() {
if (!hasNext())
throw new NoSuchElementException();
long n = 0;
boolean minus = false;
int b = readByte();
if (b == '-') {
minus = true;
b = readByte();
}
if (b < '0' || '9' < b) {
throw new NumberFormatException();
}
while (true) {
if ('0' <= b && b <= '9') {
n *= 10;
n += b - '0';
} else if (b == -1 || !isPrintableChar(b)) {
return minus ? -n : n;
} else {
throw new NumberFormatException();
}
b = readByte();
}
}
}
}