#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>
#include <map>
#include <stack>
#include <vector>
#include <set>
#include <queue>
#pragma comment (linker,"/STACK:102400000,102400000")
#define maxn 10005
#define MAXN 20005
#define mod 1000000007
#define INF 0x3f3f3f3f
#define pi acos(-1.0)
#define eps 1e-6
typedef long long ll;
using namespace std;

int n,m,ans,cnt,tot,flag;
int pp[maxn],dp[maxn][12],s;
struct Node
{
    int v,w,next;
}edge[MAXN];

void addedge(int u,int v,int w)
{
    cnt++;
    edge[cnt].v=v;
    edge[cnt].w=w;
    edge[cnt].next=pp[u];
    pp[u]=cnt;
}
void dfs(int u,int fa)
{
    int i,j,k,t,v;
    for(i=pp[u];i;i=edge[i].next)
    {
        v=edge[i].v;
        if(v==fa) continue ;
        dfs(v,u);
        for(j=m;j>=0;j--)
        {
            dp[u][j]+=dp[v][0]+2*edge[i].w;
            for(k=0;k<=j;k++)
            {
                dp[u][j]=min(dp[u][j],dp[v][k]+dp[u][j-k]+k*edge[i].w);
            }
        }
    }
}
int main()
{
    int i,j,t;
    while(~scanf("%d%d%d",&n,&s,&m))
    {
        int u,v,w;
        cnt=0;
        memset(pp,0,sizeof(pp));
        for(i=1;i<n;i++)
        {
            scanf("%d%d%d",&u,&v,&w);
            addedge(u,v,w);
            addedge(v,u,w);
        }
        memset(dp,0,sizeof(dp));
        dfs(s,0);
        ans=dp[s][m];
        printf("%d\n",ans);
    }
    return 0;
}