#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>
 
using namespace std;
 
#if __GNUC__
#include <tr1/unordered_map>
#include <tr1/unordered_set>
using namespace tr1;
#else
#include <unordered_map>
#include <unordered_set>
#endif
 
#ifdef __GNUC__
template <class T> int popcount(T n);
template <> int popcount(unsigned int n) { return __builtin_popcount(n); }
template <> int popcount(int n) { return __builtin_popcount(n); }
template <> int popcount(unsigned long long n) { return __builtin_popcountll(n); }
template <> int popcount(long long n) { return __builtin_popcountll(n); }
#else
#define __typeof__ decltype
template <class T> int popcount(T n) { return n ? 1 + popcount(n & (n - 1)) : 0; }
#endif
 
#define rep(i, n) for (int i = 0; i < (int)n; ++i)
#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define rforeach(it, c) for (__typeof__((c).rbegin()) it=(c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define COPY(dest, src) memcpy(dest, src, sizeof(dest))
 
template <class T> void max_swap(T& a, const T& b) { a = max(a, b); }
template <class T> void min_swap(T& a, const T& b) { a = min(a, b); }
 
typedef long long ll;
typedef pair<int, int> pint;
 
template <class T, class U> ostream& operator<<(ostream& os, pair<T, U>& p) { os << "( " << p.first << ", " << p.second << " )"; return os;  }

template <class T> string to_s(const T& a) { ostringstream os; os << a; return os.str(); }

bool valid_pos(int x, int y, int w, int h) { return 0 <= x && x < w && 0 <= y && y < h; }
 
template <class T> void print(T a, int n, int br = 1, const string& deli = ", ") { cout << "{ "; for (int i = 0; i < n; ++i) { cout << a[i]; if (i + 1 != n) cout << deli; } cout << " }"; while (br--) cout << endl; }
template <class T> void print(const vector<T>& v, int br = 1, const string& deli = ", ") { print(v, v.size(), br, deli); }
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) { for (int i = 0; i < h; ++i) { for (int j = 0; j < w; ++j) {	if (width != -1) cout.width(width); cout << a[i][j] << ' ';	} cout << endl; } while (br--) cout << endl; }
 
template <class T> void input(T& a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }
template <class T, class U> void input(T& a, U& b, int n) { for (int i = 0; i < n; ++i) cin >> a[i] >> b[i]; }

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { 1, 0, -1, 0 };

const int mod = 1000000007;
const double PI = acos(-1.0); 



struct P
{
	int p, c, f;
	P(int p, int c, int f)
		: p(p), c(c), f(f) { }

	bool operator<(const P& b) const
	{
		return c > b.c;
	}
};
int nono(map<string, int>& no, const string& s)
{
	if (!no.count(s))
	{
		int t = no.size();
		no[s] = t;
	}
	return no[s];
}
int main()
{
	ios::sync_with_stdio(false);

	int n, m, cap;
	while (cin >> n >> m >> cap, n)
	{
		cap *= 10;

		vector<vector<pint> > e(2 * n);	// pint(cost, to)
		bool gas[6010];
		CL(gas, 0);

		map<string, int> no;
		const int src = 0, dest = 1;

		{
			string a, b;
			cin >> a >> b;
			no[a] = src, no[b] = dest;

			for (int i = 0; i < n; ++i)
			{
				int d;
				cin >> a >> b >> d;
				int x = nono(no, a), y = nono(no, b);
				e[x].push_back(pint(d, y));
				e[y].push_back(pint(d, x));
			}

			for (int i = 0; i < m; ++i)
				cin >> a, gas[nono(no, a)] = true;
		}


		const int INF = 1 << 30;
		static int dis[6010][2010];
		for (int i = 0; i < no.size(); ++i)
			for (int j = 0; j <= cap; ++j)
				dis[i][j] = INF;

		priority_queue<P> q;
		dis[src][cap] = 0;
		q.push(P(src, 0, cap));

		int res = -1;
		while (!q.empty())
		{
			P cur = q.top();
			q.pop();

			int p = cur.p, c = cur.c, f = cur.f;
			if (c > dis[p][f])
				continue;
			else if (p == dest)
			{
				res = c;
				break;
			}

			for (int i = 0; i < e[p].size(); ++i)
			{
				int to = e[p][i].second;
				int d = e[p][i].first;
				int nc = c + d;
				int nf = f - d;
				if (nf >= 0)
				{
					if (gas[to])
						nf = cap;
					if (nc < dis[to][nf])
					{
						dis[to][nf] = nc;
						q.push(P(to, nc, nf));
					}
				}
			}
		}

		cout << res << endl;
	}
}

Measured memory_bytes: 63000