#include <stdio.h>
#include <string.h>
#define maxn 0x3f3f3f3

char str[155][35];
int map[155][155], dis[155], visited[155];

void Dijkstra(int start, int n)
{
    int mind, pre;
    for(int i = 0; i<n; i++)
    {
        dis[i] = map[start][i];
        visited[i] = 0;
    }
    visited[start] = 1;

    for(int i = 0; i<n; i++)
    {
        mind = maxn;
        for(int j = 0; j<n; j++)
        {
            if(mind > dis[j] && !visited[j])
            {
                mind = dis[j];
                pre = j;
            }
        }
        visited[pre] = 1;
        for(int j = 0; j<n; j++)
        {
            if(dis[j] > dis[pre]+map[pre][j] && !visited[j])
                dis[j] = dis[pre]+map[pre][j];
        }
    }
}

int Find(char * stra, int & m)
{
    int i;
    for(i = 0; i<m; i++)
    {
        if(strcmp(str[i], stra) == 0)
            break ;
    }
    if(i == m)
    {
        strcpy(str[i], stra);
        m++;
    }

    return i;
}

int main()
{
    int n, m, x;
    char start[35], finish[35];
    char stra[35], strb[35];
    while(scanf("%d", &n)!=EOF && n!=-1)
    {
        m = 0;
        scanf("%s%s", start, finish);
        Find(start, m);    Find(finish, m);
        for(int i = 0; i<155; i++)
        {
            for(int j = 0; j<155; j++)
            {
                if(i == j)
                    map[i][j] = 0;
                else
                    map[i][j] = maxn;
            }
        }
        while(n--)
        {
            scanf("%s%s%d", stra, strb, &x);
            if(map[Find(stra, m)][Find(strb, m)] > x || map[Find(strb, m)][Find(stra, m)] >x)
            {
                map[Find(stra, m)][Find(strb, m)] = x;
                map[Find(strb, m)][Find(stra, m)] = x;
            }
        }

        Dijkstra(Find(start, m), m);

        if(visited[Find(finish, m)])
            printf("%d\n", dis[Find(finish, m)]);
        else
            printf("-1\n");

    }
    return 0;
}