fr.cpp
#include <algorithm>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
using namespace std;
#define DEBUG(x) cout << ">>> " << #x << " : " << x << endl;
#define REP(i,a) for (int i = 0; i < (a); ++i)
#define FOR(i,a,b) for (int i = (a); i <= (b); ++i)
#define FORD(i,a,b) for (int i = (a); i >= (b); --i)
inline bool EQ(double a, double b) { return fabs(a-b) < 1e-9; }
const int INF = 1<<29;
typedef long long ll;
#define maxN 1005
int n,c;
int u,v,w;
vector<int> edges[maxN];
vector<ll> prizes[maxN];
int father[maxN];
ll fatherprize[maxN];
ll sum;
ll comp(int u){
if(edges[u].size()==1) return fatherprize[u];
ll ans = 0;
REP(i,edges[u].size()){
if(edges[u][i]==father[u]) continue;
father[edges[u][i]]=u;
fatherprize[edges[u][i]]=prizes[u][i];
ans += comp(edges[u][i]);
}
ans = min(ans,fatherprize[u]);
return ans;
}
int main() {
while(scanf("%d%d",&n,&c)==2){
sum = 0;
c--;
REP(i,n){ edges[i].clear(); prizes[i].clear(); }
REP(i,n-1){
scanf("%d%d%d",&u,&v,&w);
u--; v--;
edges[u].push_back(v); edges[v].push_back(u);
prizes[u].push_back(w); prizes[v].push_back(w);
}
REP(i,edges[c].size()){
father[edges[c][i]]=c;
fatherprize[edges[c][i]]=prizes[c][i];
sum += comp(edges[c][i]);
}
printf("%lld\n",sum);
}
return 0;
}