#include<cstdio>

#include<iostream>

#include<cstring>

#define R register int

using namespace std;

struct edge {

    int v,w,nxt;

}e[];

int n,cnt,s;

int fir[];

long long ans,mx[];

inline void add(int u,int v,int w) {e[++cnt].v=v,e[cnt].w=w,e[cnt].nxt=fir[u],fir[u]=cnt;}

inline int g() {

    R ret=,fix=; register char ch; while(!isdigit(ch=getchar())) fix=ch=='-'?-:fix;

    do ret=ret*+(ch^); while(isdigit(ch=getchar())); return ret*fix;

}

void dfs(int u,int fa) {

    //cout<<u<<" "<<fa<<endl;

    for(R i=fir[u];i;i=e[i].nxt) {

        R v=e[i].v;

        if(v==fa) continue;

        dfs(v,u); mx[u]=max(mx[u],mx[v]+e[i].w);

    }

    for(R i=fir[u];i;i=e[i].nxt) {

        R v=e[i].v;

        if(v==fa) continue;

        ans+=mx[u]-(mx[v]+e[i].w);

    }

}

signed main() {

    n=g(),s=g();

    for(R i=;i<n;++i){R u=g(),v=g(),w=g(); add(u,v,w),add(v,u,w);}

    dfs(s,); printf("%lld\n",ans);

}