#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const LL mod=1e9+7;
const int N=1e5+6;
const int inf=0x3f3f3f3f;
int n,cnt,num;
map<string,int>mp;
struct Edge
{
    int to,next,val;
};
Edge edge[N];
int dis[200],p[200][200],flag[200];
int dijkstra()
{
    memset(flag,0,sizeof(flag));
    dis[1]=0;
    for(int i = 2;i < num;i ++)
    {
        dis[i]=p[1][i];
    }
    flag[1]=1;
    int pre;
    for(int j = 1;j < num;j ++)
    {
        int mmin = inf;
    for(int i = 1;i < num;i ++)
    {
        if(flag[i] == 0 &&dis[i] < mmin)
        {
            mmin=dis[i];
            pre=i;
        }
    }
    if(mmin == inf)break;
    flag[pre] = 1;
    for(int i =1;i < num;i++)
    {
        if(flag[i] == 0 &&dis[i]>dis[pre]+p[pre][i])
        {
            dis[i]=dis[pre]+p[pre][i];
        }
    }
    }
}
int main()
{
    while(1)
    {
        scanf("%d",&n);
        if(n==-1)break;
        for(int i=1;i<200;i++)
        {
            for(int j=1;j<200;j++)
            {
                if(i==j)p[i][j]=0;
                else p[i][j]=inf;
            }
        }
        memset(dis,inf,sizeof(dis));
        string str1,str2;
        int v;
        mp.clear();
        cin>>str1>>str2;
        int x=0;
        if(str1==str2)x=1;
        else {mp[str1]=1;
        mp[str2]=2;}
        num=3;
        for(int i=0;i < n;i++)
        {
            cin>>str1>>str2>>v;
            if(!mp[str1])mp[str1]=num++;
            if(!mp[str2])mp[str2] = num++;
            int pos1=mp[str1],pos2=mp[str2];
           p[pos2][pos1]=p[pos1][pos2]=min(p[pos1][pos2],v);
        }
       if(x==0){
        dijkstra();
        if(dis[2]==inf)printf("-1\n");
        else printf("%d\n",dis[2]);
       }
       else printf("0\n");
    }
    return 0;
}