#include<cstdio>
#include<iostream>
#include<cstring>
#include<string>
#include<algorithm>
#include<map>
using namespace std;
map<string,int>mp;//映射
string s,e;//開始站和终点站
int n;
const int INF=10010100;
int m[160][160],d[160],used[160],k;
void dij()///dij模板
{
fill(d,d+k+1,INF);//注意这里是k个,不是n个,n仅仅是路数,不是点数,一開始由于这个RE了好几次
memset(used,0,sizeof(used));
d[1]=0;
while(1)
{
int v=-1;
for(int u=1; u<=k; u++)
if(!used[u]&&(v==-1||d[u]<d[v]))
v=u;
if(v==-1)
break;
if(d[v]==INF)
break;
used[v]=1;
for(int u=1; u<=k; u++)
if(d[u]>d[v]+m[v][u])
d[u]=d[v]+m[v][u];
}
}
int main()
{
//int n;
while(cin>>n)
{
if(n==-1)
break;
else
{
mp.clear();
for(int i=0; i<=155; i++)//建图,初始化
for(int j=0; j<=155; j++)
{
if(i==j)
m[i][j]=0;
else
m[i][j]=INF;
}
int v;
k=1;
string s1,s2;
cin>>s>>e;
//用map映射给站名标记,起始站为1,终点站为2
mp[s]=k++;
mp[e]=k++;
for(int i=0; i<n; i++)
{
cin>>s1>>s2>>v;
if(!mp[s1])
mp[s1]=k++;
if(!mp[s2])
mp[s2]=k++;
if(v<m[mp[s1]][mp[s2]])
m[mp[s1]][mp[s2]]=m[mp[s2]][mp[s1]]=v;
}
//cout<<mp[e]<<endl;
if(s==e)
cout<<"0
";
else
{
dij();
if(d[2]==INF)
cout<<"-1
";
else
cout<<d[2]<<endl;
}
}
}
return 0;
}