visita.cpp

#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e4 + 5;

int dist[maxn];
vector<pair<int, int>> adj[maxn];

void dfs(int x, int pai){
	for(auto[v, w] : adj[x]) if(v!=pai)
		dist[v] = dist[x]+w, dfs(v, x);
}

int main(){
	int n, ini, fim; cin >> n >> ini >> fim;
	for(int i = 0; i < n-1; i++){
		int a, b, c; cin >> a >> b >> c;
		adj[a].push_back({b, c});
		adj[b].push_back({a, c});
	}

	dfs(ini, ini);
	cout << dist[fim] << '\n';
}