#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize ("Ofast")
#define sze(x) (ll)(x.size())
typedef long long ll;
typedef pair<ll , ll> pll;
const ll maxn = (1 << 20) + 17 , inf = 2e16;
ll n , s , t;
vector<pll> adj[maxn];
vector<ll> dis[maxn] , bfs;
ll g[maxn] , k[22] , d[22] , e[22] , dp[maxn][22];
void BFS(ll r , bool f = false){
bfs.clear();
dis[r].assign(n , inf);
dis[r][r] = 0;
g[r] = 0;
bfs.push_back(r);
ll x = 0;
while(x < sze(bfs)){
ll v = bfs[x++];
for(auto p : adj[v]){
ll i = p.first , t = p.second;
if(dis[r][i] < dis[r][v] + 1) continue;
if(f){
g[i] = g[v];
if(t != -1){
g[i] ^= (1 << t);
d[t] = v;
}
}
dis[r][i] = dis[r][v] + 1;
bfs.push_back(i);
}
}
return;
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
memset(dp , 63 , sizeof(dp));
cin>>n>>s>>t; s--; t--;
ll m = 0;
for(ll i = 1 ; i < n ; i++){
ll v , u , w;
cin>>v>>u>>w; v--; u--; w--;
if(w != -1){
k[m] = w;
adj[v].push_back({u , m}); adj[u].push_back({v , m});
m++;
} else {
adj[v].push_back({u , w}); adj[u].push_back({v , w});
}
}
BFS(s , true);
if(g[t] == 0){
cout<<dis[s][t]<<'\n';
return 0;
}
for(ll j = 0 ; j < m ; j++){
e[j] = g[k[j]] | g[d[j]];
BFS(d[j]);
if(e[j] == 0){
dp[(1 << j)][j] = dis[s][k[j]] + dis[d[j]][k[j]];
}
}
ll lm = (1 << m);
for(ll mask = 1 ; mask < lm ; mask++){
for(ll j = 0 ; j < m ; j++){
if(mask & (1 << j)) continue;
if((e[j] & mask) != e[j]) continue;
ll h = inf;
for(ll i = 0 ; i < m ; i++){
if(!(mask & (1 << i))) continue;
h = min(h , dp[mask][i] + dis[d[i]][k[j]] + dis[d[j]][k[j]]);
}
dp[mask ^ (1 << j)][j] = min(dp[mask ^ (1 << j)][j] , h);
}
}
// cout<<dp[2][1]<<' '<<dp[6][2]<<' '<<dp[7][0]<<'\n';
// cout<<dis[d[0]][t]<<'\n';
ll ans = inf;
for(ll mask = 1 ; mask < lm ; mask++){
if((g[t] & mask) != g[t]) continue;
ll h = inf;
for(ll i = 0 ; i < m ; i++){
if(!(mask & (1 << i))) continue;
// cout<<mask<<' '<<i<<'\n';
h = min(h , dp[mask][i] + dis[d[i]][t]);
}
ans = min(ans , h);
}
cout<<(ans == inf ? -1 : ans)<<'\n';
return 0;
}
