救救孩子！！！！！

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define ll long long
using namespace std;
const int maxn=500050;
struct node{
	int to,val,next;
}e[maxn*2];
ll fa[maxn],size[maxn],cd[maxn],depth[maxn],head[maxn];
ll n,s,a,b,t,cnt,tag,ans;
queue<int>q;
inline void read(ll &x){
	static char rc;static int flag;
	rc=getchar();flag=1;x=0;
	while(rc<'0'||rc>'9')
	  flag=(rc=='-'?-1:1),rc=getchar();
	while(rc<='9'&&rc>='0')
	  x=x*10+rc-'0',rc=getchar();
	x=x*flag;
}
inline void add(int u,int v,int w){
	e[++cnt].next=head[u];
	e[cnt].to=v;
	e[cnt].val=w;
	head[u]=cnt;
}
ll judge_big(ll a,ll b){return a>b?a:b;}
void dfs(int now){
	for(int i=head[now];i;i=e[i].next){
		int son=e[i].to;
		if(son==fa[now])continue;
		fa[son]=now;cd[now]++;
		depth[son]=depth[now]+e[i].val;
		tag=judge_big(tag,depth[son]);
		dfs(son);
	}
}
void work(int now){
	ll jojo=tag-size[now];
	ans+=jojo;
	for(int i=head[now];i;i=e[i].next){
		int son=e[i].to;
		if(son==fa[now])continue;
		size[son]+=jojo;
		work(son);
	}
}
int main(){
	read(n),read(s);
	fa[s]=s;depth[s]=0;
	for(int i=1;i<n;++i){
		read(a),read(b),read(t);
		add(a,b,t);add(b,a,t);
	}
	dfs(s);
	for(int i=1;i<=n;++i)
	  if(!cd[i])q.push(i),size[i]=depth[i];
	while(!q.empty()){
		int now=q.front();q.pop();
		size[fa[now]]=judge_big(size[fa[now]],size[now]);
		cd[fa[now]]--;
		if(!cd[fa[now]])q.push(fa[now]);
	}
	work(s);
	cout<<ans<<endl;
}