#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize ("Ofast")
#define sze(x) (int)(x.size())
typedef long long ll;
typedef pair<ll , ll> pll;
typedef pair<int , int> pii;
typedef pair<pii , int> piii;
const ll maxn = (1 << 20) + 17 , inf = 2e8;
int n , s , t;
pii adj[maxn << 1];
vector<piii> ed;
int dg[maxn] , st[maxn] , ft[maxn] , x[maxn];
int dis[22][maxn];
int bfs[maxn] , sz = 0;
int g[maxn] , k[22] , d[22] , e[22] , f[22][22] , dp[maxn][22] , ind[22];
void rBFS(int r , int h){
sz = 0;
dis[h][r] = 0;
g[r] = 0;
bfs[sz++] = r;
int x = 0;
while(x < sz){
int v = bfs[x++];
for(int e = st[v] ; e < ft[v] ; e++){
pii p = adj[e];
int i = p.first , t = p.second;
if(dis[h][i] < dis[h][v] + 1) continue;
g[i] = g[v];
if(t != -1){
g[i] ^= (1 << t);
d[t] = v;
}
dis[h][i] = dis[h][v] + 1;
bfs[sz++] = i;
}
}
return;
}
void BFS(int r , int h){
sz = 0;
dis[h][r] = 0;
g[r] = 0;
bfs[sz++] = r;
int x = 0;
while(x < sz){
int v = bfs[x++];
for(int e = st[v] ; e < ft[v] ; e++){
pii p = adj[e];
int i = p.first , t = p.second;
if(dis[h][i] < dis[h][v] + 1) continue;
dis[h][i] = dis[h][v] + 1;
bfs[sz++] = i;
}
}
return;
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
memset(dp , 63 , sizeof(dp));
memset(dis , 63 , sizeof(dis));
cin>>n>>s>>t; s--; t--;
int m = 0;
for(int i = 1 ; i < n ; i++){
int v , u , w;
cin>>v>>u>>w; v--; u--; w--;
dg[v]++; dg[u]++;
if(w != -1){
k[m] = w;
ed.push_back({{v , u} , m});
m++;
} else {
ed.push_back({{v , u} , -1});
}
}
x[0] = st[0] = 0; ft[0] = dg[0];
for(int i = 1 ; i < n ; i++){
x[i] = st[i] = ft[i - 1]; ft[i] = st[i] + dg[i];
}
for(auto p : ed){
int v = p.first.first , u = p.first.second , w = p.second;
adj[x[v]++] = {u , w}; adj[x[u]++] = {v , w};
}
rBFS(s , m);
if(g[t] == 0){
cout<<dis[m][t]<<'\n';
return 0;
}
for(int j = 0 ; j < m ; j++){
e[j] = g[k[j]] | g[d[j]];
BFS(d[j] , j);
if(e[j] == 0){
dp[(1 << j)][j] = dis[m][k[j]] + dis[j][k[j]];
}
}
for(int i = 0 ; i < m ; i++){
for(int j = 0 ; j < m ; j++){
f[i][j] = dis[i][k[j]] + dis[j][k[j]];
}
}
int lm = (1 << m);
for(int mask = 3 ; mask < lm ; mask++){
int bp = 0;
for(int j = 0 ; j < m ; j++){
if(mask & (1 << j)) ind[bp++] = j;
}
if(bp == 1) continue;
for(int jj = 0 ; jj < bp ; jj++){
int j = ind[jj];
if((e[j] & mask) != e[j]) continue;
int h = inf , msk = mask ^ (1 << j);
for(int ii = 0 ; ii < bp ; ii++){
int i = ind[ii];
if(i == j) continue;
h = min(h , dp[msk][i] + f[i][j]);
}
dp[mask][j] = h;
}
}
int ans = inf;
for(int mask = 1 ; mask < lm ; mask++){
if((g[t] & mask) != g[t]) continue;
int h = inf;
for(int i = 0 ; i < m ; i++){
if(!(mask & (1 << i))) continue;
// cout<<mask<<' '<<i<<'\n';
h = min(h , dp[mask][i] + dis[i][t]);
}
ans = min(ans , h);
}
cout<<(ans == inf ? -1 : ans)<<'\n';
return 0;
}
