.cpp

#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
#define ft first
#define sd second

int n, s1, s2;
struct Edge{
	int to;
	int cost;
	Edge(int t=0, int c=0):to(t), cost(c){}
};
vector<vector<Edge>> p;
bool chk[110'000];
pii zero = {0, 0};
pii dfs(int now, pii ret){
	if(chk[now]) return zero;
	chk[now] = true;
	if(now == s2) return ret;
	pii tmp;
	for(auto e: p[now]){
		int next = e.to;
		int ncost = e.cost;
		if((tmp = dfs(next, {ret.ft + ncost, max(ret.sd, ncost)})).ft != 0)
			return tmp;
	}
	return zero;
}
int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	cin>>n>>s1>>s2;
	p.resize(n+1);
	for(int i=0; i<n-1; i++){
		int u, v, c;
		cin>>u>>v>>c;
		p[u].emplace_back(v, c);
		p[v].emplace_back(u, c);
	}
	
	pii ans = dfs(s1, zero);
	cout<<ans.ft - ans.sd;
}