#include<iostream>

#include<map>

#include<cstdio>

#include<cstring>

#include<string>

using namespace std;

#define INF 99999999

int m1[][];

map<string,long long>ma;

int dis[];

int vis[];int c;

void di()

{   memset(vis,,sizeof(vis));

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

         dis[i]=m1[][i];

    vis[]=;

    for(int i=;i<c-;i++)

    {

        int minn=INF;

        int u;

        for(int j=;j<=c;j++)

        {

            if(vis[j]==&&dis[j]<minn)

            {

                u=j;

                minn=dis[j];

            }

        }

        vis[u]=;

        for(int j=;j<=c;j++)

        {

            if(vis[j]==&&dis[u]+m1[u][j]<dis[j])

            {

                dis[j]=dis[u]+m1[u][j];

            }

        }

    }

}

int main()

{

 int n;

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

 {    c=;

      ma.clear();

     string s1,s2;

    int ok=;

     cin>>s1>>s2;if(s1==s2){ok=;}

     ma[s1]=++c;

     ma[s2]=++c;

     int time1;

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

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

     {

         if(i==j)m1[i][j]=;

         else m1[i][j]=INF;

     }

     while(n--)

     {

         cin>>s1>>s2>>time1;

         if(ma[s1]==)ma[s1]=++c;

         if(ma[s2]==)ma[s2]=++c;

         if(time1<m1[ ma[s1] ][ ma[s2]  ])

         {

             m1[ ma[s1] ][ ma[s2]  ]=m1[ ma[s2] ][ ma[s1] ]=time1;

         }

     }

     di();

  if(!ok)printf("0\n");

   else {

     if(dis[]!=INF)

     printf("%d\n",dis[]);

     else

        printf("-1\n");

   }

 }

return ;

}