using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    static void Main()
    {
        var c = NList;
        var (n, m, k) = (c[0], c[1], c[2]);
        var s = ReadLine().Split();
        var map = NMap(m);

        var scc = new SCCGraph(n);
        foreach (var edge in map) scc.AddEdge(edge[0], edge[1]);
        var sccList = scc.SCC();
        var idlist = new int[n];
        for (var i = 0; i < sccList.Length; ++i) foreach (var id in sccList[i]) idlist[id] = i;

        var nn = sccList.Length;
        var tree = new HashSet<int>[nn];
        for (var i = 0; i < tree.Length; ++i) tree[i] = new HashSet<int>();
        var endcount = new int[nn];
        foreach (var edge in map)
        {
            var from = idlist[edge[0]];
            var to = idlist[edge[1]];
            if (from != to)
            {
                tree[from].Add(to);
                ++endcount[to];
            }
        }
        var strlist = new List<char>[nn];
        for (var i = 0; i < nn; ++i)
        {
            strlist[i] = new List<char>();
            foreach (var id in sccList[i]) strlist[i].Add(s[id][0]);
            strlist[i].Sort();
        }
        var dp = new List<char>[nn][];
        for (var i = 0; i < dp.Length; ++i)
        {
            dp[i] = new List<char>[k + 1];
            for (var j = 0; j < dp[i].Length; ++j) dp[i][j] = new List<char>();
        }
        var q = new Queue<int>();
        for (var i = 0; i < nn; ++i) if (endcount[i] == 0)
        {
            q.Enqueue(i);
            for (var j = 1; j <= strlist[i].Count; ++j) dp[i][j].AddRange(strlist[i].Take(j));
        }
        while (q.Count > 0)
        {
            var cur = q.Dequeue();
            foreach (var next in tree[cur])
            {
                --endcount[next];
                if (endcount[next] == 0) q.Enqueue(next);
                var previ = -1;
                for (var i = 1; i < dp[cur].Length; ++i)
                {
                    if (dp[cur][i].Count == 0)
                    {
                        if (previ < 0) previ = i - 1;
                        if (dp[cur][previ].Count + strlist[next].Count < i) break;
                        dp[next][i] = Min(dp[next][i], SmallestSub(dp[cur][previ].Concat(strlist[next]).ToList(), i));
                    }
                    else
                    {
                        var nlist = new List<char>();
                        if (previ >= 0) dp[next][i] = Min(dp[next][i], SmallestSub(dp[cur][previ].Concat(strlist[next]).ToList(), i));
                        dp[next][i] = Min(dp[next][i], SmallestSub(dp[cur][i].Concat(strlist[next]).ToList(), i));
                    }
                }
            }
        }
        var res = new List<char>();
        for (var i = 0; i < dp.Length; ++i) res = Min(res, dp[i][k]);
        if (res.Count > 0) WriteLine(string.Concat(res));
        else WriteLine("-1");
    }
    static List<char> Min(List<char> a, List<char> b)
    {
        if (b.Count == 0) return a;
        if (a.Count == 0) return b;
        for (var i = 0; i < a.Count; ++i)
        {
            if (a[i] < b[i]) return a;
            if (a[i] > b[i]) return b;
        }
        return a;
    }
    static List<char> SmallestSub(List<char> list, int k)
    {
        var table = new int[26][];
        for (var i = 0; i < table.Length; ++i)
        {
            table[i] = Enumerable.Repeat(int.MaxValue / 2, list.Count).ToArray();
            var c = (char)('a' + i);
            for (var j = list.Count - 1; j >= 0; --j)
            {
                if (j < list.Count - 1) table[i][j] = table[i][j + 1];
                if (list[j] == c) table[i][j] = j;
            }
        }
        var res = new List<char>();
        var last = 0;
        for (var i = 0; i < k; ++i)
        {
            for (var c = 0; c < table.Length; ++c)
            {
                if (table[c][last] + (k - i - 1) < list.Count)
                {
                    res.Add((char)(c + 'a'));
                    last = table[c][last] + 1;
                    break;
                }
            }
        }
        return res;
    }
    class SCCGraph
    {
        private int _n;
        private List<(int from, int to)> edges;
        public SCCGraph(int n)
        {
            _n = n;
            edges = new List<(int, int)>();
        }
        public int NumVertices() { return _n; }
        public void AddEdge(int from, int to) { edges.Add((from, to )); }
        public (int, int[]) SCCIds()
        {
            var g = new CSR<int>(_n, edges);
            var nowOrd = 0;
            var groupNum = 0;
            var visited = new List<int>(_n);
            var low = new int[_n];
            var ord = Enumerable.Repeat(-1, _n).ToArray();
            var ids = new int[_n];
            void DFS(int v)
            {
                low[v] = ord[v] = nowOrd++;
                visited.Add(v);
                for (var i = g.Start[v]; i < g.Start[v + 1]; ++i)
                {
                    var to = g.EList[i];
                    if (ord[to] == -1)
                    {
                        DFS(to);
                        low[v] = Math.Min(low[v], low[to]);
                    }
                    else low[v] = Math.Min(low[v], ord[to]);
                }
                if (low[v] == ord[v])
                {
                    while (true)
                    {
                        var u = visited.Last();
                        visited.RemoveAt(visited.Count - 1);
                        ord[u] = _n;
                        ids[u] = groupNum;
                        if (u == v) break;
                    }
                    ++groupNum;
                }
            }
            for (var i = 0; i < _n; ++i) if (ord[i] == -1) DFS(i);
            for (var i = 0; i < ids.Length; ++i) ids[i] = groupNum - 1 - ids[i];
            return (groupNum, ids);
        }
        public List<int>[] SCC()
        {
            var (groupNum, list) = SCCIds();
            var counts = new int[groupNum];
            foreach (var x in list) ++counts[x];
            var groups = new List<int>[groupNum];
            for (var i = 0; i < groups.Length; ++i) groups[i] = new List<int>(counts[i]);
            for (var i = 0; i < _n; ++i) groups[list[i]].Add(i);
            return groups;
        }
    }
    // 有向辺のリスト
    class CSR<E>
    {
        public int[] Start { get; private set; }
        public E[] EList { get; private set; }
        public CSR(int n, List<(int, E)> edges)
        {
            Start = new int[n + 1];
            EList = new E[edges.Count];
            foreach (var e in edges) ++Start[e.Item1 + 1];
            for (var i = 1; i <= n; ++i) Start[i] += Start[i - 1];
            var counter = (int[])Start.Clone();
            foreach (var e in edges)
            {
                EList[counter[e.Item1]++] = e.Item2;
            }
        }
    }
}