fr.cpp

#include <stdio.h>
#include <string.h>
#include <vector>
#define mp make_pair
#define pb push_back
#define INF 99999999
#define REP(A,B) for(int (A) = 0; (A) < (B); A++)
using namespace std;
 
vector<pair<int,int> > dest[1111];
pair<int,int> from[1111];
vector<pair<int,int> > desc[1111];
bool visited[1111];
 
void scan(int p) {
	visited[p] = true;
	for(int i = 0; i < dest[p].size(); i++) {
		int v = dest[p][i].first;
		if(!visited[v]) {
			visited[v] = true;
//			desc[p].pbi(mp(v, dest[p][i].second));
			from[v] = mp(p, dest[p][i].second);
			scan(v);
		}
	}
}
int dp[1111];
int solve(int p) {
	if(desc[p].size() == 0) return INF;
	if(dp[p] == -1) {
		int ans = 0;
		for(int i = 0; i < desc[p].size(); i++) {
			int tgt = desc[p][i].first;
			int price = desc[p][i].second;
			ans += min(price, solve(tgt));
		}
		dp[p] = ans;
	}
	return dp[p];
}
 
int main() {
	int n, c;
	while(scanf("%d %d", &n, &c) == 2) {
		REP(i, n) {
			dest[i].clear();
			desc[i].clear();
		}
		REP(i, n) visited[i] = false;
		memset(dp, -1, sizeof(dp));
		REP(i, n-1) {
			int u,v,w;
			scanf("%d %d %d", &u, &v, &w);
			u--; v--;
			dest[u].pb(mp(v,w));
			dest[v].pb(mp(u,w));
		}
		c--;
		from[c].first = -1;
 
		scan(c);
		//REP(i, n) if(i != c) printf("from[%d]=%d\n", i, from[i].first);
		for(int i = 0; i < n; i++) {
			if(i == c) continue;
			desc[from[i].first].pb(mp(i, from[i].second));
//			printf("descs of %d: %d\n", i+1, desc[i].size());
		}
		//REP(i, n) printf("descs of %d: %d\n", i+1, desc[i].size());
	//	REP(i, n) printf("water for %d from %d, closing %d\n", i+1, from[i].first+1, from[i].second);
		printf("%d\n", solve(c));
	}
	return 0;
}