/*
* 主要是用一個map和一個時間戳變量來分配id,其他都是模板
*/
#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2e2 + 10;
const int MAXM = 2e4 + 10;
const int INF = 0x3f3f3f3f;
struct E{
int to, w, nxt;
}edge[MAXM];
int tot, tim; //tim爲id分配器,從1開始分配
int head[MAXN];
priority_queue<pair<int, int>> Q;
map<string, int> M;
int dis[MAXN];
bool use[MAXN];
int n, s, e;
string S, E;
inline void clear(){
tot = tim = 0;
memset(head, -1, sizeof head);
while(!Q.empty()) Q.pop();
M.clear();
memset(dis, INF, sizeof dis); //未初始化完
memset(use, false, sizeof use);
}
inline void addedge(int u, int v, int w){
edge[tot].to = v;
edge[tot].w = w;
edge[tot].nxt = head[u];
head[u] = tot++;
}
inline void dijkstra(){
Q.push({0, s});
while(!Q.empty()){
auto it = Q.top();
int id = it.second;
Q.pop();
if(use[id]) continue;
use[id] = true;
for(int i = head[id]; ~i; i = edge[i].nxt){
int to = edge[i].to;
int w = edge[i].w;
if(dis[id] + w < dis[to]){
dis[to] = dis[id] + w;
Q.push({-dis[to], to});
}
}
}
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
//cout << setiosflags(ios::fixed) << setprecision(1); //保留小數點後1位
//cout << setprecision(1); //保留1位有效數字
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
while(cin >> n){
if(n == -1) break;
clear();
cin >> S >> E;
if(M[S] == 0) M[S] = ++tim; //分配id
if(M[E] == 0) M[E] = ++tim; //分配id
s = M[S];
e = M[E];
dis[s] = 0;
for(int i = 1; i <= n; ++i){
string strs, stre;
int w;
cin >> strs >> stre >> w;
if(M[strs] == 0) M[strs] = ++tim; //分配id
if(M[stre] == 0) M[stre] = ++tim; //分配id
int u = M[strs];
int v = M[stre];
addedge(u, v, w);
addedge(v, u, w);
}
dijkstra();
if(dis[e] == INF) cout << -1 << endl;
else cout << dis[e] << endl;
}
return 0;
}