// 2011アジア地区予選 D : Long Distance Taxi

#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <queue>

using namespace std;

class Node{
public:
	int p, q, c;
	Node(int p, int q, int c) : p(p), q(q), c(c) {}
	bool operator < (const Node &nd) const { return c > nd.c; }
};

const int INF = 1000000007;
typedef vector< vector<Node> > graph;

vector<int> getCost(const graph &g, int src, int cap){
	vector<bool> visit(g.size(), false);
	vector<int> res(g.size(), 10*cap+1);
	priority_queue< Node > qu; qu.push(Node(src, src, 0));
	res[src] = 0;
	while(!qu.empty()){
		Node nd = qu.top(); qu.pop();
		int pos = nd.q, cost = nd.c;
		if(visit[pos]) continue;
		for(int i=0;i<g[pos].size();i++){
			int next = g[pos][i].q;
			if(cost + g[pos][i].c < res[next]){
				res[next] = cost + g[pos][i].c;
				qu.push(Node(pos, next, res[next]));
			}
		}
	}
	return res;
}

int dijkstra(const graph &g, int src, int dst){
	vector<bool> visit(g.size(), false);
	vector<int> res(g.size(), INF);
	priority_queue< Node > qu; qu.push(Node(src, src, 0));
	res[src] = 0;
	while(!qu.empty()){
		Node nd = qu.top(); qu.pop();
		int pos = nd.q, cost = nd.c;
		if(visit[pos]) continue;
		for(int i=0;i<g[pos].size();i++){
			int next = g[pos][i].q;
			if(cost + g[pos][i].c < res[next]){
				res[next] = cost + g[pos][i].c;
				qu.push(Node(pos, next, res[next]));
			}
		}
	}
	return res[dst] < INF ? res[dst] : -1;
}

int main(){
	int N, M, cap;
	while(cin >> N >> M >> cap, N){
		string src, dst; cin >> src >> dst;
		map<string, int> mp;
		graph g1(2*N, vector<Node>());
		int idx = 0;
		for(int i=0;i<N;i++){
			string c1, c2; int d;
			cin >> c1 >> c2 >> d;
			if(!mp.count(c1)) mp[c1] = idx++;
			if(!mp.count(c2)) mp[c2] = idx++;
			g1[mp[c1]].push_back(Node(mp[c1], mp[c2], d));
			g1[mp[c2]].push_back(Node(mp[c2], mp[c1], d));
		}
		vector<int> LPG(M+2);
		for(int i=1;i<=M;i++){
			string s; cin >> s;
			LPG[i] = mp[s];
		}
		
		if(!mp.count(src)){ cout << -1 << endl; continue; }
		if(!mp.count(dst)){ cout << -1 << endl; continue; }

		LPG[0  ] = mp[src];
		LPG[M+1] = mp[dst];

		graph g2(M+2, vector<Node>());
		for(int i=0;i<M+2;i++){
			vector<int> vi = getCost(g1, LPG[i], cap);
			for(int j=0;j<M+2;j++){
				if(vi[LPG[j]] <= 10*cap)
					g2[i].push_back(Node(i, j, vi[LPG[j]]));
			}
		}

		cout << dijkstra(g2, 0, M+1) << endl;
	}
}