#include <bits/stdc++.h>
using namespace std;

template<class T>
bool chmax(T& a, const T& b) {
    if (a < b) { a = b; return true; }
    return false;
}
template<class T>
bool chmin(T& a, const T& b) {
    if (b < a) { a = b; return true; }
    return false;
}

// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

// std::vector Declaration and Initialization
template<typename T>
vector<T> make_vector(size_t a, T x) { return vector<T>(a, x); }
template<typename T, typename U, typename... Ts>
auto make_vector(size_t a, U b, Ts... ts) {
    return vector<decltype(make_vector<T>(b,ts...))>(a, make_vector<T>(b, ts...));
}

// std::vector Input
template<typename T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto &e : v) is >> e;
    return is;
}

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::array Debug
template<typename T, size_t n>
ostream& operator<<(ostream& os, const array<T, n>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::deque Debug
template<typename T>
ostream& operator<<(ostream& os, const deque<T>& d) {
    os << "[";
    bool a = 1;
    for (auto e : d) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << " " << p.second << ")";
    return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
    os << "{";
    bool a = 1;
    for (auto e : mp) {
        os << (a ? "" : " ");
        os << e.first << ":" << e.second;
        a = 0;
    }
    os << "}";
    return os;
}

// std::tuple Debug
template<int N, class Tuple>
void out(ostream& os, const Tuple& t){}
template<int N, class Tuple, class H, class ...Ts>
void out(ostream& os, const Tuple& t) {
    if (N) os << " ";
    os << get<N>(t);
    out<N+1,Tuple,Ts...>(os, t);
}
template<class ...Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
    os << "(";
    out<0,tuple<Ts...>,Ts...>(os, t);
    os << ")";
    return os;
}

// Debug
#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl

// Weighted edge
template<typename T>
struct edge {
    int src, to;
    T cost;

    edge() {}
    edge(int to, T cost) : src(-1), to(to), cost(cost) {}
    edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

    friend ostream& operator<<(ostream& os, const edge& e) {
        return os << "(" << e.src << "->" << e.to << ":" << e.cost << ")";
    }
};

using LL = int64_t;

#define fs first
#define sc second

const int64_t MOD = 1e9+7;



int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    while (true) {
        int n, m, cap; cin >> n >> m >> cap;
        cap *= 10;
        if (n == 0) break;

        map<string,int> cities;
        string src, dst; cin >> src >> dst;
        cities[src] = cities[dst] = -1;

        vector<string> u(n), v(n);
        vector<int> d(n);
        for (int i = 0; i < n; ++i) {
            cin >> u[i] >> v[i] >> d[i];
            cities[u[i]] = cities[v[i]] = -1;
        }
        map<string,bool> s;
        for (int i = 0; i < m; ++i) {
            string t; cin >> t;
            s[t] = true;
            cities[t] = -1;
        }

        int cnt = 0;
        for (auto& tp : cities) {
            tp.second = cnt++;
        }

        map<int,string> citymap;
        for (const auto& tp : cities) {
            citymap[tp.second] = tp.first;
        }

        vector<vector<edge<int>>> G(cnt);
        for (int i = 0; i < n; ++i) {
            G[cities[u[i]]].emplace_back(cities[v[i]], d[i]);
            G[cities[v[i]]].emplace_back(cities[u[i]], d[i]);
        }

        int ans = numeric_limits<int>::max();

        auto dist = make_vector<int>(cnt, cap+1, numeric_limits<int>::max());
        dist[cities[src]][cap] = 0;
        using Pi = pair<int, pair<int,int>>;
        priority_queue<Pi, vector<Pi>, greater<Pi>> que;
        que.emplace(0, make_pair(cities[src], cap));

        while (!que.empty()) {
            int cost; pair<int,int> p;
            tie(cost, p) = que.top();
            que.pop();
            int v, cp; tie(v, cp) = p;
            if (dist[v][cp] < cost) continue;
            if (v == cities[dst]) {
                ans = cost;
                break;
            }
            for (auto &e : G[v]) {
                int nxtCost = cost + e.cost,
                    nxtCap = cp - e.cost;
                if (nxtCap < 0) continue;
                if (s[citymap[e.to]]) nxtCap = cap;
                if (dist[e.to][nxtCap] > nxtCost) {
                    dist[e.to][nxtCap] = nxtCost;
                    que.emplace(nxtCost, make_pair(e.to, nxtCap));
                }
            }
        }

        cout << (ans == numeric_limits<int>::max() ? -1 : ans) << endl;
    }

    return 0;
}



Measured memory_bytes: 52288