#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
#include<cstdlib>
#include<vector>
using namespace std;
#define INF 1<<30
vector<int> e[2005],w[2005];
int n,r;
int dp[2005];
void dfs(int u,int fa)
{
    int ans=0;
    for(int i=0;i<e[u].size();i++)
    {
        int v=e[u][i];
        if(v==fa)
            continue;
        dfs(v,u);
        ans+=min(dp[v],w[u][i]);
    }
    if(ans)
        dp[u]=ans;
}
int main()
{
    int x,y,z;
    while(scanf("%d%d",&n,&r)!=EOF)
    {
        if(n==0&&r==0)
            break;
        for(int i=0;i<=n;i++)
        {
            e[i].clear();
            w[i].clear();
            dp[i]=INF;
        }
        for(int i=0;i<n-1;i++)
        {
            scanf("%d%d%d",&x,&y,&z);
            e[x].push_back(y);
            e[y].push_back(x);
            w[x].push_back(z);
            w[y].push_back(z);
        }
        if(n==1)
        {
            printf("0\n");
            continue;
        }
        dfs(r,-1);
        printf("%d\n",dp[r]);
    }
    return 0;
}