#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <algorithm>
#include <map>
#define MAXX 155
#define INF 1000000000
using namespace std;

int d[MAXX],mp[MAXX][MAXX],visit[MAXX];

void Dijkstra(int n)
{
    memset(visit,0,sizeof(visit));
    int i,y;
    for(i=1;i<=n;i++)
    {
        d[i] = mp[1][i];
    }
    d[1] = 0;
    visit[1]=1;
    for(i=1; i<=n; i++)
    {
        int m=INF,x;
        for(y=1; y<=n; y++)
        {
            if(!visit[y] && d[y]<=m)
            {
                m = d[x = y];
            }
        }
        if(m == INF)break;
        visit[x]=1;
        for(y=1; y<=n; y++)
        {
            if(!visit[y] && d[y]>d[x]+mp[x][y])
            {
                d[y]=d[x]+mp[x][y];
            }
        }
    }
}

int main()
{
    int n,m,i,j;
    char tmp[32],tmp1[32];
    map<string,int>car;

    while(scanf("%d",&n)!=EOF&&n!=-1)
    {
        bool flag=false;
        for(i=0; i<MAXX; i++)
            for(j=0; j<MAXX; j++)
                mp[i][j]=INF;
        car.clear();
        scanf("%s%s",tmp,tmp1);
        if(strcmp(tmp,tmp1)==0)
        {
            flag=true;
        }
        car[tmp]=1;
        car[tmp1]=2;
        int count = 3 ;
        int di=0;
        for(i=0;i<n;i++)
        {
            scanf("%s%s%d",tmp,tmp1,&di);
            if(!car[tmp])
            {
                car[tmp]=count++;
            }
            if(!car[tmp1])
            {
                car[tmp1]=count++;
            }
            if(mp[car[tmp]][car[tmp1]] > di)
            {
                mp[car[tmp1]][car[tmp]]=mp[car[tmp]][car[tmp1]]=di;
            }
        }
        if(flag)
        {
            printf("0\n");
            continue;
        }
        Dijkstra(count-1);
        if(d[2]==INF)printf("-1\n");
        else
        printf("%d\n",d[2]);
    }
    return 0;
}