#include<bits/stdc++.h>

 using namespace std;

 typedef long long ll;

 const int maxn =  + ;

 const int INF = 0x3f3f3f3f;

 int Map[maxn][maxn];

 int v[maxn], d[maxn];

 int n, m;

 set<string>cnt;

 map<string, int>G;

 int GetID(string s)

 {

     if(cnt.count(s))return G[s];

     cnt.insert(s);

     return G[s] = cnt.size();

 }

 void dijkstra(int s, int t)

 {

     memset(v, , sizeof(v));

     for(int i = ; i <= n; i++)d[i] = (i == s ?  : INF);

     for(int i = ; i < n; i++)

     {

         int x = -, m = INF;

         for(int i = ; i <= n; i++)if(!v[i] && d[i] <= m)m = d[x = i];

         v[x] = ;

         for(int i = ; i <= n; i++)

         {

             if(d[i] > d[x] + Map[x][i])

             {

                 d[i] = d[x] + Map[x][i];

             }

         }

     }

     if(d[t] == INF)d[t] = -;

     cout<<d[t]<<endl;

 }

 int main()

 {

     while(scanf("%d", &n) != EOF && n != -)

     {

         int u, v, w;

         string s1,s2;

         cnt.clear();

         G.clear();

         cin >> s1 >> s2;

         int s = GetID(s1);

         int t = GetID(s2);

         memset(Map, INF, sizeof(Map));

         while(n--)

         {

             cin >> s1 >> s2 >> w;

             Map[GetID(s1)][GetID(s2)] = Map[GetID(s2)][GetID(s1)] = min(Map[GetID(s1)][GetID(s2)], w);

         }

         n = cnt.size();

         dijkstra(s, t);

     }

 }