#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
#define X first
#define Y second
#define mins(a, b) (a = min(a,b))
const int MXN = 1e6+2, MXM = 20, inf = 1e9;
int n, m, s, t, ctr, id[MXN], vec[MXN];
vector<pii> g[MXN];
int dis[MXM*2+1][MXN], dp[1<<MXM][MXM], mask[MXM*2+1][MXN], door[MXN];
inline void assign_id(int v) {
if(id[v]==-1)
vec[id[v]=ctr++] = v;
}
void dfs1(int v, int p=0) {
for(auto [u, w] : g[v])
if(u!=p) {
if(w) {
door[id[w]] = v;
assign_id(v);
}
dfs1(u, v);
}
}
void dfs(int wh, int v, int p=0) {
for(auto [u, w] : g[v])
if(u!=p) {
dis[wh][u] = dis[wh][v]+1;
mask[wh][u] = mask[wh][v] | (w ? (1<<id[w]) : 0);
dfs(wh, u, v);
}
}
inline bool is_sub(int x, int y) { return (x&y)==x; }
int32_t main() {
cin.tie(0); cout.tie(0); ios_base::sync_with_stdio(0);
memset(id, -1, sizeof(id));
cin >> n >> s >> t;
for(int i=0, u,v,w; i<n-1; i++) {
cin >> u >> v >> w;
g[u].push_back({v, w});
g[v].push_back({u, w});
if(w) assign_id(w);
}
m = ctr;
dfs1(s);
assign_id(s);
for(int i=0; i<ctr; i++) dfs(i, vec[i]);
if(!mask[id[s]][t]) {
cout << dis[id[s]][t] << '\n';
return 0;
}
for(int msk=0; msk<(1<<m); msk++)
fill(dp[msk], dp[msk]+m, inf);
for(int i=0; i<m; i++)
if(!mask[id[s]][vec[i]] && !mask[i][door[i]])
dp[1<<i][i] = dis[id[s]][vec[i]] + dis[i][door[i]];
for(int msk=1; msk<(1<<m)-1; msk++)
for(int i=0; i<m; i++) if(msk>>i&1)
for(int j=0; j<m; j++) if(!(msk>>j&1)) {
int v = door[i], u = vec[j], w = door[j];
if(is_sub(mask[id[v]][u], msk) && is_sub(mask[id[u]][w], msk|(1<<j)))
mins(dp[msk|(1<<j)][j], dp[msk][i] + dis[id[v]][u] + dis[id[u]][w]);
}
int ans = inf;
for(int msk=1; msk<(1<<m); msk++)
for(int i=0; i<m; i++) if((msk>>i&1) && is_sub(mask[id[door[i]]][t], msk))
mins(ans, dp[msk][i] + dis[id[door[i]]][t]);
cout << (ans==inf ? -1 : ans) << '\n';
return 0;
}
