#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include <cmath>

 #include<stack>

 #include<vector>

 #include<map>

 #include<set>

 #include<queue>

 #include<algorithm>

 #define mod=1e9+7;

 using namespace std;

 typedef long long LL;

 const int INF = ;

 const int maxn=;

 map<string,int> mp;

 int d[maxn][maxn];

 int main(){

     int n,i,j,k,w;

     string st,en,s1,s2;

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

         mp.clear();

         int cnt=;

         for(i=;i<maxn;i++){

             for(j=;j<maxn;j++){

                 if(i==j) d[i][j]=;

                 else d[i][j]=INF;

             }

         }

         cin>>st>>en;

         if(!mp[st]) mp[st]=cnt++;

         if(!mp[en]) mp[en]=cnt++;

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

             cin>>s1>>s2>>w;

             if(!mp[s1]) mp[s1]=cnt++;

             if(!mp[s2]) mp[s2]=cnt++;

             if(d[mp[s1]][mp[s2]]>w) d[mp[s1]][mp[s2]]=d[mp[s2]][mp[s1]]=w;

         }

         for(k=;k<cnt;k++)

          for(i=;i<cnt;i++)

           for(j=;j<cnt;j++)

            d[i][j]=min(d[i][j],d[i][k]+d[k][j]);

            if(d[mp[st]][mp[en]]==INF) printf("-1\n");

            else printf("%d\n",d[mp[st]][mp[en]]);

     }

     return ;

 }