fr.cpp

#include <cstdio>
#include <vector>
#include <iostream>
#include <string>
#include <algorithm>
#include <cstring>
#include <set>
#include <vector>
 
using namespace std;
 
struct edge
{
    edge(int bb, int cc) { b = bb; w = cc; }
    int b, w;
    bool operator<(edge const& e) const { return w < e.w; }
};
 
vector<vector<edge> > v;
 
int go(int node, int prev)
{
    int res = 0;
    for (int i = 0; i < v[node].size(); ++i)
        if (v[node][i].b != prev)
            res += min(v[node][i].w, go(v[node][i].b, node));
 
//    cout << "node " << node << " returned " << res << endl;
    return res ? res : 10000000;
}
 
int main()
{
    int n, c;
 
 
 
    while (scanf("%d %d\n", &n, &c) > 0)
    {
        v.clear();
        v.resize(n+1);
        int u, vv, w;
        for (int i = 0; i < n-1; ++i)
        {
            scanf("%d %d %d", &u, &vv, &w);
            v[u].push_back(edge(vv, w));
            v[vv].push_back(edge(u, w));
        }
 
        printf("%d\n", go(c, 0));
 
    }
    return 0;
}