// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
#ifdef KURUMI
#include "algo/debug.h"
#endif
#define endl '\n'
#define fi first
#define se second
#define sz(v) (int)v.size()
#define all(v) v.begin(), v.end()
#define filter(v) v.resize(unique(all(v)) - v.begin())
#define dbg(x) "[" #x << " = " << x << "]"
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
template<typename T1, typename T2> T2 rand(T1 l, T2 r) {
return uniform_int_distribution<T2>(l, r)(rng);
}
template<typename T1, typename T2> T2 wrand(T1 l, T2 r, int seed) {
if(seed == 0) return rand(l, r);
else return (seed > 0 ? max(rand(l, r), wrand(l, r, seed - 1)) : min(rand(l, r), wrand(l, r, seed + 1)));
}
template<typename T> bool maximize(T &a, T b) {
if(a < b) {
a = b;
return true;
}else return false;
}
template<typename T> bool minimize(T &a, T b) {
if(a > b) {
a = b;
return true;
}else return false;
}
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> tp3;
int read_int(){
int result = 0;
char ch;
ch = getchar();
while (true) {
if (ch >= '0' && ch <= '9') break;
ch = getchar();
}
result = ch-'0';
while (true) {
ch = getchar();
if (ch < '0' || ch > '9') break;
result = result*10 + (ch - '0');
}
return result;
}
const int N = 1e6 + 3;
const int M = 20;
int n, m, s, t;
vector<int> useful, only;
vector<tp3> edge;
vector<int> adj[N];
bool rolled = false;
struct DisjointSet {
vector<int> lab, save;
vector<pair<int&, int>> history;
DisjointSet () {}
DisjointSet (int n) : lab(n + 3, -1) {}
int root(int u) {
if(lab[u] < 0) return u;
return (rolled ? root(lab[u]) : lab[u] = root(lab[u]));
}
bool unite(int u, int v) {
u = root(u); v = root(v);
if(u == v) return false;
if(-lab[u] < -lab[v]) swap(u, v);
if(rolled) {
history.emplace_back(lab[u], lab[u]);
history.emplace_back(lab[v], lab[v]);
}
lab[u] += lab[v];
lab[v] = u;
return true;
}
bool same(int u, int v) {
return root(u) == root(v);
}
void persist() {
save.push_back(sz(history));
}
void rollback() {
int t = save.back();
while(sz(history) > t) {
history.back().fi = history.back().se;
history.pop_back();
}
}
} dsu;
void input() {
n = read_int();
// m = read_int();
s = read_int();
t = read_int();
dsu = DisjointSet(n);
for(int i = 1; i < n; i++) {
int u, v, lock;
u = read_int();
v = read_int();
lock = read_int();
adj[u].push_back(v);
adj[v].push_back(u);
if(lock) {
m++;
edge.emplace_back(u, v, lock);
useful.push_back(u);
useful.push_back(v);
only.push_back(u);
only.push_back(v);
only.push_back(lock);
}else dsu.unite(u, v);
}
}
const int LOG = 21;
const int INF = 0x3f3f3f3f;
int timer = 0, answer = INF;
int tin[N], h[N], id[N], oid[N], predist[100][100];
int spt[2 * N][LOG], dp[1 << M][2 * M + 3];
int merge(int x, int y) {
return tin[x] < tin[y] ? x : y;
}
void prepare(int u, int p) {
tin[u] = ++timer;
spt[timer][0] = u;
for(int v : adj[u]) {
if(v == p) continue;
h[v] = h[u] + 1;
prepare(v, u);
spt[++timer][0] = u;
}
}
int lca(int u, int v) {
int l = tin[u], r = tin[v];
if(l > r) swap(l, r);
int b = 31 - __builtin_clz(r - l + 1);
return merge(spt[l][b], spt[r - (1 << b) + 1][b]);
}
int distance(int u, int v) {
return h[u] + h[v] - 2 * h[lca(u, v)];
}
void process() {
prepare(1, -1);
for(int j = 1; j < LOG; j++) {
for(int i = 1; i + (1 << j) - 1 <= timer; i++) {
spt[i][j] = merge(spt[i][j - 1], spt[i + (1 << (j - 1))][j - 1]);
}
}
if(dsu.same(s, t)) return cout << distance(s, t) << endl, void();
sort(all(useful)); filter(useful);
int k = sz(useful);
for(int i = 0; i < k; i++) id[useful[i]] = i;
sort(all(only)); filter(only);
for(int i = 0; i < sz(only); i++) oid[only[i]] = i;
for(int i = 0; i < sz(only); i++) {
for(int j = 0; j < sz(only); j++) {
predist[i][j] = distance(only[i], only[j]);
}
}
memset(dp, 0x3f, sizeof(dp));
for(int i = 0; i < m; i++) {
int u, v, lock; tie(u, v, lock) = edge[i];
if(dsu.same(s, lock) && dsu.same(lock, u)) dp[1 << i][id[u]] = distance(s, lock) + distance(lock, u);//, cout << dbg(s) << dbg(lock) << dbg(u) << endl;
if(dsu.same(s, lock) && dsu.same(lock, v)) dp[1 << i][id[v]] = distance(s, lock) + distance(lock, v);//, cout << dbg(s) << dbg(lock) << dbg(v) << endl;
}
rolled = true; dsu.persist();
for(int mask = 0; mask < (1 << m); mask++) {
vector<int> one, zero;
for(int i = 0; i < m; i++) {
if(mask >> i & 1) {
one.push_back(i);
int u, v; tie(u, v, ignore) = edge[i];
dsu.unite(u, v);
}
else zero.push_back(i);
}
for(int i : one) {
int u, v; tie(u, v, ignore) = edge[i];
int ru = dsu.root(u), rv = dsu.root(v);
for(int j : zero) {
int nu, nv, lock; tie(nu, nv, lock) = edge[j];
int rnu = dsu.root(nu), rnv = dsu.root(nv), rlock = dsu.root(lock);
if(ru == rlock) {
if(rlock == rnu) minimize(dp[mask ^ (1 << j)][id[nu]], dp[mask][id[u]] + predist[oid[u]][oid[lock]] + predist[oid[nu]][oid[lock]]);
if(rlock == rnv) minimize(dp[mask ^ (1 << j)][id[nv]], dp[mask][id[u]] + predist[oid[u]][oid[lock]] + predist[oid[nv]][oid[lock]]);
}
if(rv == rlock) {
if(rlock == rnu) minimize(dp[mask ^ (1 << j)][id[nu]], dp[mask][id[v]] + predist[oid[v]][oid[lock]] + predist[oid[nu]][oid[lock]]);
if(rlock == rnv) minimize(dp[mask ^ (1 << j)][id[nv]], dp[mask][id[v]] + predist[oid[v]][oid[lock]] + predist[oid[nv]][oid[lock]]);
}
}
}
for(int i = 0; i < k; i++) {
if(dsu.same(useful[i], t)) minimize(answer, dp[mask][i] + distance(useful[i], t));
}
dsu.rollback();
}
cout << (answer == INF ? -1 : answer) << endl;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
#define task "TREEMAZE"
if(fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
int testcase = 1; // cin >> testcase;
for(int i = 1; i <= testcase; i++) {
input();
process();
}
cerr << "Saa, watashtachi no deeto hajimemashou" << endl;
cerr << "Atarashii kiseki wo koko kara hajimeru shining place nee mou ichido kimi to..." << endl;
cerr << "Time elapsed: " << (1000.0 * clock() / CLOCKS_PER_SEC) << "ms.\n";
return 0;
}
