#include <cstdio>

 #include <string>

 #include <cstring>

 #include <iostream>

 #include <algorithm>

 using namespace std;

 int dp[][];

 struct node

 {

     int u,v,w,next;

 }edge[];

 int first[],t,flag[];

 int n,m;

 void CL()

 {

     t = ;

     memset(first,-,sizeof(first));

     memset(flag,,sizeof(flag));

 }

 void add(int u,int v,int w)

 {

     edge[t].u = u;

     edge[t].v = v;

     edge[t].w = w;

     edge[t].next = first[u];

     first[u] = t ++;

 }

 void dfs(int u)

 {

     int i,v,j,k;

     flag[u] = ;

     for(i = first[u];i != -;i = edge[i].next)

     {

         v = edge[i].v;

         if(flag[v]) continue;

         dfs(v);

         for(j = m;j >= ;j --)

         {

             dp[u][j] += dp[v][] + *edge[i].w;

             for(k = ;k <= j;k ++)

             {

                 dp[u][j] = min(dp[u][j],dp[u][j-k] + dp[v][k] + k*edge[i].w);

             }

         }

     }

 }

 int main()

 {

     int s,u,v,w,i;

     while(scanf("%d%d%d",&n,&s,&m)!=EOF)

     {

         CL();

         memset(dp,,sizeof(dp));

         for(i = ;i < n;i ++)

         {

             scanf("%d%d%d",&u,&v,&w);

             add(u,v,w);

             add(v,u,w);

         }

         dfs(s);

         printf("%d\n",dp[s][m]);

     }

     return ;

 }