#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define ll long long
#define rep(i,x,y) for(ll i=(x);i<=(y);i++)
#define repl(i,x,y) for(ll i=(x);i<(y);i++)
#define repd(i,x,y) for(ll i=(x);i>=(y);i--)
using namespace std;

const ll N=5e5+5;
const ll Inf=1e18;

ll n,m,ans,f[N];
ll cnt,to[N<<1],edge[N<<1],nxt[N<<1],head[N];

inline ll read() {
	ll x=0;char ch=getchar();bool f=0;
	while(ch>'9'||ch<'0'){if(ch=='-')f=1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
	return f?-x:x;
}

void ins(ll x,ll y,ll z) {
	to[++cnt]=y;edge[cnt]=z;nxt[cnt]=head[x];head[x]=cnt;
}

void dfs(ll x,ll fa) {
	for(ll i=head[x];i;i=nxt[i]) if(to[i]!=fa) dfs(to[i],x),f[x]=max(f[x],f[to[i]]+edge[i]);
	
	for(ll i=head[x];i;i=nxt[i]) if(to[i]!=fa) ans+=f[x]-f[to[i]]-edge[i];
}

int main() {
	n=read(),m=read();
	repl(i,1,n) {
		ll x=read(),y=read(),z=read();
		ins(x,y,z);ins(y,x,z);
	}
	
	dfs(m,0);
	
	printf("%lld",ans);

	return 0;
}