#include<iostream>

#include<string>

#include<cstring>

using namespace std;

#define MaxSize 100

using namespace std;

typedef struct ArcNode

{

    int adjvex;                 //该边所指向的结点的位置（也就是编号）

    struct ArcNode *nextarc;    //指向下一条边的指针

    int info;                   //

}ArcNode;

typedef struct

{

    char data;                  //顶点信息

    ArcNode *firstarc;          //指向第一条边的指针

}VNode;

typedef struct

{

    VNode adjlist[MaxSize];

    int n, e;                    //顶点数、边数

}AGraph;                        //图的邻接表类型

int visit[MaxSize];

int Locate(AGraph *AG, char c)

{

    for (int i = ; i < AG->n; i++)

    {

        if (AG->adjlist[i].data == c)

            return i;

    }

}

int nodenum = ;

bool DFS(AGraph *G, int v,int w,int k)

{

    ArcNode *p;

    visit[v] = ++nodenum;

    if (v == w && k == )//置标志位1代表已访问

        return true;

    else

        if (k > )

        {

            p = G->adjlist[v].firstarc;

            while (p)

            {

                if (visit[p->adjvex] == &&DFS(G,p->adjvex,w,k-))

                {

                    return true;

                }

                visit[p->adjvex] = ;

                nodenum--;

                p = p->nextarc;

            }

        }

    return false;

}

//创建无向图的邻接表

void createAGraph2(AGraph *&AG, int t, int p)

{

    int i, j, k;

    ArcNode *q;

    AG->n = t;

    AG->e = p;

    string b;

    cin >> b;

    for (i = ; i < AG->n; i++)

    {

        AG->adjlist[i].data = b[i];

        AG->adjlist[i].firstarc = NULL;

    }

    string cc;

    for (k = ; k < AG->e; ++k)

    {

        cin >> cc;

        //头插法

        i = Locate(AG, cc[]);

        j = Locate(AG, cc[]);

        q = new ArcNode;

        q->adjvex = j;

        q->nextarc = AG->adjlist[i].firstarc;

        AG->adjlist[i].firstarc = q;

        q = new ArcNode;

        q->adjvex = i;

        q->nextarc = AG->adjlist[j].firstarc;

        AG->adjlist[j].firstarc = q;

    }

}

AGraph *AG;

int main()

{

    int n, m,k;

    while (cin >> n >> m >>k&& k!=||n !=  || m != )

    {

        AG = new AGraph;

        createAGraph2(AG, n, m);

        string a;

        cin >> a;//查询的两个顶点

        if (DFS(AG, Locate(AG,a[]),Locate(AG, a[]),k))

            cout << "YES" << endl;

        else

            cout << "NO" << endl;

    }

    return ;

}