#include<bits/stdc++.h>	
using namespace std;
int n,m,k;
int visited[27];
int start=0;
queue<int> Q;
int BFS(int G[][27],int x){
	Q.push(start);
	Q.push(-1);
	int l=0;
	while(!Q.empty()){
		int z=Q.front();
		Q.pop();
		if(z==-1){
			l++;
			if(!Q.empty()){
				z=Q.front();
				Q.pop();
				Q.push(-1);
			}
			else break;
		}
		if(visited[z]==1) continue;
		visited[z]=1;
		for(int i=0;i<26;i++){
			if(G[z][i]==1){
				char p=z+'a';
				char q=i+'a';
				cout<<p<<"->"<<q<<endl;
				if(q==x){
					return 1;
				}
				Q.push(i);
			}
		}
		if(l==k){
			break;
		}
	}
	return -1;
}
int found=0;
void DFS(vector<int> rem,int v,int G[][27],char x){
	char c=v+'a';
	visited[v]=1;
	for(int i=0;i<26;i++){
		if(found==0 and G[v][i]==1 and visited[i]==0){
			char z=i+'a';
			cout<<c<<"->"<<z<<endl;
			if(z==x){
				found=1;
				return ;
			}
			DFS(rem,i,G,x);
		}
	}
}
int SEARCH(int G[][27],int x){
	int a=BFS(G,x);
	if(a==1) return 1;
	vector<int> rem;
	while(!Q.empty()){
		int z=Q.front();
		if(z!=-1 and visited[z]==0) rem.push_back(z);
		Q.pop();
	}
	sort(rem.begin(),rem.end());
	found=0;
	for(int i=0;i<rem.size();i++){
		if(visited[rem[i]]==0 and found==0){
			DFS(rem,rem[i],G,x);
		}
	}
	if(found==1) return 1;
	for(int i=0;i<n;i++){
		if(visited[i]==0){
			start=i;
			int p=SEARCH(G,x);
			if(p==1) return 1;
		}
	}
	return -1;
}
int main(){
	cin>>n>>m>>k;
	int G[27][27];
	memset(G,0,sizeof(G));
	for(int i=0;i<m;i++){
		char x,y;
		cin>>x>>y;
		G[x-'a'][y-'a']=1;
	}
	char x;
	cin>>x;
	memset(visited,0,sizeof(visited));
	cout<<SEARCH(G,x)<<endl;
}