//#pragma warning disable
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System;
using System.Numerics;
using System.Threading.Tasks;
using static System.Math;
using static System.Console;
class E { static void Main() => new K(); }
class K
{
int F() => int.Parse(ReadLine());
long FL() => int.Parse(ReadLine());
int[] G() => ReadLine().Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries).Select(int.Parse).ToArray();
long[] GL() => ReadLine().Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries).Select(long.Parse).ToArray();
public const int MOD = 1000000007;
public K()
{
//SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
Solve();
//Out.Flush();
}
int V, E, k, M;
char[] c;
int[] which;
List<int>[] es, res, fs;
string[] strs;
// dp[i,n] = i番目のSCCから初めてn文字とる
string[,] dp;
void Solve()
{
var I = G();
V = I[0];
E = I[1];
k = I[2];
c = Console.ReadLine().Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries).Select(s => s[0]).ToArray();
es = new List<int>[V];
res = new List<int>[V];
for (var i = 0; i < V; i++) es[i] = new List<int>();
for (var i = 0; i < V; i++) res[i] = new List<int>();
for (var i = 0; i < E; i++)
{
I = G();
int a = I[0] - 1, b = I[1] - 1;
es[a].Add(b);
res[b].Add(a);
}
StronglyConnectedComponents();
dp = new string[M, k + 1];
for (var u = M - 1; u >= 0; u--)
{
var len = strs[u].Length;
dp[u, 0] = "";
for (var n = 1; n <= k; n++)
{
if (n <= len) dp[u, n] = strs[u].Substring(0, n);
if (fs[u].Count != 0)
{
for (var m = 1; m <= n && m <= len; m++)
{
var best = dp[fs[u][0], n - m];
foreach (var v in fs[u].Skip(1)) if (Compare(best, dp[v, n - m]) > 0) best = dp[v, n - m];
var tmp = strs[u].Substring(0, m) + best;
if (Compare(dp[u, n], tmp) > 0) dp[u, n] = tmp;
}
}
if (dp[u, n] != null && dp[u, n].Length != n) dp[u, n] = null;
Console.WriteLine("dp[{0}, {1}] = {2}", u, n, dp[u, n]);
}
}
Console.WriteLine("M = {0}", M);
for (var i = 0; i < V; i++) Console.WriteLine("f[{0}] = {1}", i, which[i]);
for (var i = 0; i < M; i++) foreach (var w in fs[i]) Console.WriteLine("{0} -> {1}", i, w);
for (var i = 0; i < M; i++) Console.WriteLine("S[{0}] = {1}", i, strs[i]);
string min = null;
for (var i = 0; i < M; i++) if (Compare(min, dp[i, k]) > 0) min = dp[i, k];
Console.WriteLine(min ?? "-1");
}
// null is max
int Compare(string a, string b)
{
if (a == b) return 0;
if (a == null) return 1;
if (b == null) return -1;
return a.CompareTo(b);
}
public void StronglyConnectedComponents()
{
var mark = new bool[V];
var stack = new Stack<int>();
Action<int> dfs = null;
dfs = v =>
{
mark[v] = true;
foreach (var w in es[v]) if (!mark[w]) dfs(w);
stack.Push(v);
};
for (var v = 0; v < V; v++) if (!mark[v]) dfs(v);
var scc = new List<HashSet<int>>();
mark = new bool[V];
which = new int[V];
Action<int, HashSet<int>> rdfs = null;
rdfs = (v, set) =>
{
set.Add(v);
mark[v] = true;
foreach (var w in res[v]) if (!mark[w]) rdfs(w, set);
};
while (stack.Count > 0)
{
var v = stack.Pop();
if (mark[v]) continue;
var set = new HashSet<int>();
rdfs(v, set);
scc.Add(set);
foreach (var w in set) which[w] = M;
M++;
}
fs = new List<int>[M];
var tmp = new List<char>[M];
for (var v = 0; v < M; v++) fs[v] = new List<int>();
for (var v = 0; v < M; v++) tmp[v] = new List<char>();
for (var v = 0; v < V; v++) tmp[which[v]].Add(c[v]);
strs = new string[M];
for (var v = 0; v < M; v++)
{
tmp[v].Sort();
strs[v] = new string(tmp[v].ToArray());
}
for (var v = 0; v < V; v++) foreach (var w in es[v])
{
int a = which[v], b = which[w];
if (a != b) fs[a].Add(b);
}
}
}