#include<bits/stdc++.h>
using namespace std ;
typedef long long ll ;
#define el '\n'
const ll maxn = 1e6 + 100 ;
const ll maxk = 23 ;
ll n , spt[maxn][maxk] , h[maxn] , par[maxn] , Close[maxn] ;
ll st , en ;
vector<pair<ll,ll>> adj[maxn] ;
ll frst[maxn] ;
ll ans = 0 ;
vector<ll> tour ;
void dfs_lca(ll u , ll p){
par[u] = p ;
h[u] = (p == -1) ? 0 : h[p]+1 ;
frst[u] = tour.size() ;
tour.push_back(u) ;
for(auto [v,w] : adj[u]){
if(v == p){Close[u] = w;continue;}
dfs_lca(v,u) ;
tour.push_back(u) ;
}
return ;
}
ll get_lca(ll u , ll v){
ll l = min(frst[u],frst[v]) , r = max(frst[u],frst[v])+1 ;
ll lg = 31-__builtin_clz(r-l) ;
if(h[spt[l][lg]] < h[spt[r-(1<<lg)][lg]]){return spt[l][lg];}
else{return spt[r-(1<<lg)][lg];}
}
ll good = 0 ;
ll ok = 1 ;
map<pair<ll,pair<ll,ll>>,bool> mp ;
void f(ll S , ll E){
if(!ok){return;}
if(mp[{good,{S,E}}]){good = 0;return;}
mp[{good,{S,E}}] = 1 ;
ll LCA = get_lca(S,E) ;
ll A = S ;
ll cnt = 0 ;
ll k = 0 ;
while(A != LCA){
if(Close[A] == -1){
cnt++ ; A = par[A];
}
else{
f(S,Close[A]) ;
ll x = Close[A] ;
Close[A] = -1 ;
good++ ;
f(x,A) ;
f(A,E) ;
return ;
}
}
while(A != E){
ll V = 0 ;
for(auto [v,w] : adj[A]){
if(v == par[A]){continue;}
if(get_lca(v,E) != v){continue;}
V = v ;
}
if(Close[V] == -1){
cnt++ ;A = V;
}
else{
f(S,Close[V]) ;
ll x = Close[V] ;
Close[V] = -1 ;
good++ ;
f(x,A) ;
f(A,E) ;
return ;
}
}
ans += cnt ;
return ;
}
void solve(){
cin>>n ;
cin>>st>>en ; st-- ; en-- ;
for(ll i = 0 ; i < n-1 ; i++){
ll u , v , w ;
cin>>u>>v>>w ; u-- ; v-- ; w-- ;
adj[u].push_back({v,w}) ; adj[v].push_back({u,w}) ;
}
dfs_lca(st,-1) ;
for(ll i = 0 ; i < tour.size() ; i++){
spt[i][0] = tour[i] ;
}
for(ll x = 1 ; x < maxk ; x++){
for(ll i = 0 ; i < tour.size() ; i++){
if(tour.size() < i + (1<<x)){break;}
if(h[spt[i][x-1]] < h[spt[i+(1<<(x-1))][x-1]]){spt[i][x] = spt[i][x-1];}
else{spt[i][x] = spt[i+(1<<(x-1))][x-1];}
}
}
f(st,en) ;
cout<<(ok?ans:-1)<<el ;
return ;
}
int main(){
//std::ios_base::sync_with_stdio(false) , cin.tie(nullptr) ;
solve() ;
}
