fr.cpp

#include <iostream>
#include <set>
#include <stdio.h>
#include <utility>
#include <map>
#include <string>
#include <sstream>
#include <algorithm>
#include <vector>
using namespace std;
 
int dfs(const vector<vector<int> > & G, const vector<vector<int> > & eff, int node, int parEff, int parent){
	int e = 0;
	if(G[node].size() == 1){
		return parEff;
	}
	for(int i=0; i<G[node].size(); ++i){
		if(G[node][i] != parent){
			e += dfs(G, eff, G[node][i], eff[node][i], node);
		}
	}
	return min(e, parEff);
}
 
int solve(const vector<vector<int> > & G, const vector<vector<int> > & eff, int root){
	int e = 0;
	for(int i=0; i<G[root].size(); ++i){
		e += dfs(G, eff, G[root][i], eff[root][i], root);
	}
	return e;
}
 
 
int main(){
	int n, root;
	while(cin >> n >> root){
		vector<vector<int> > G(n+1);
		vector<vector<int> > eff(n+1);
		for(int i=0; i<n-1; ++i){
			int u, v, w;
			cin >> u >> v >> w;
			G[u].push_back(v);
			G[v].push_back(u);
			eff[u].push_back(w);
			eff[v].push_back(w);
		}
		cout << solve(G, eff, root) << '\n';
	}
	return 0;
}