#include<cstdio>#include<cstring>#include<vector>#include<queue>#include<algorithm>using namespace std;vector<pair<int,int> > edge[100010];int step[100100];int vis[100010];int bfs(int &s){ int Max=0; memset(vis,0,sizeof(vis)); queue<int> Q; Q.push(s);step[s]=0; while(!Q.empty()){ int fr=Q.front();Q.pop(); for(int i=0;i<edge[fr].size();i++){ int to=edge[fr][i].first,w=edge[fr][i].second; if(vis[to]) continue; step[to]=step[fr]+w; if(step[to]>Max){ Max=step[to]; s=to; } vis[to]=1; Q.push(to); } }return Max;}int main(){ int n,s,i,a,b,w; while(scanf("%d%d",&n,&s)!=EOF){ int sum=0; for(i=0;i<n-1;i++){ scanf("%d%d%d",&a,&b,&w); sum+=2*w; edge[a].push_back(make_pair(b,w)); edge[b].push_back(make_pair(a,w)); } bfs(s); int mm=bfs(s); printf("%dn",sum-mm); }}
