// In the Name of Allah
#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast,unroll-loops,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4.1,avx,avx2,sse4.2,popcnt,tune=native")
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define pb push_back
#define pp pop_back
#define all(x) x.begin(), x.end()
const int N = 1e6 + 12, M = 20;
vector<pii> g[N];
int n, s, t, h[N], f[N][M];
pii par[N];
vector<int> v[M + 3];
bool don[N], op[N];
void ip() {
cin >> n >> s >> t;
for (int i = 1; i < n; i++) {
int u, v, w;
cin >> u >> v >> w;
g[u].pb({v, w});
g[v].pb({u, w});
}
}
int lca(int u, int v) {
if (h[u] < h[v])
swap(u, v);
for (int i = 0; i < M; i++)
if (((h[u] - h[v]) >> i) & 1)
u = f[u][i];
if (u == v)
return u;
for (int i = M - 1; ~i; --i)
if (f[u][i] != f[v][i])
u = f[u][i], v = f[v][i];
return f[u][0];
}
int dis(int u, int v) {
return h[u] + h[v] - 2 * h[lca(u, v)];
}
int dfs(int a, int b, int c = 0) {
if (don[b] == true) {
cout << -1;
exit(0);
}
don[b] = true;
v[c].pb(a);
par[a] = {a, 0};
while (!v[c].empty()) {
int u = v[c].back();
v[c].pp();
for (auto i: g[u])
if (i.F != par[u].F)
v[c].pb(i.F), par[i.F] = {u, i.S};
}
int u = b;
vector<pii> d;
while (u != a) {
d.pb(par[u]);
u = par[u].F;
}
reverse(all(d));
int ans = 0;
int pl = a;
for (auto i: d)
if (i.S && !op[i.S]) {
ans += dfs(pl, i.S, c + 1);
ans += dis(i.S, i.F);
pl = i.F;
}
ans += dis(pl, b);
don[b] = false;
op[b] = true;
return ans;
}
void dfs1(int u) {
for (auto i: g[u])
if (i.F != f[u][0]) {
f[i.F][0] = u;
h[i.F] = h[u] + 1;
for (int j = 1; j < M; ++j)
f[i.F][j] = f[f[i.F][j - 1]][j - 1];
dfs1(i.F);
}
}
void solve() {
for (int i = 0; i < M; i++)
f[1][i] = 1;
dfs1(1);
cout << dfs(s, t);
}
int32_t main() {
ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
ip(), solve();
return 0;
}
