#include<bits/stdc++.h>
typedef long long ll;
#define pb push_back
#define fr first
#define sc second
#define endl '\n'
using namespace std;
const int inf=1e9;
int n,k,root;
vector<pair<int,int>>komsu[10023];
int dp[10023][2][10023];
int sub[10023];
void dfs(int pos,int par,int val){
int m=0;
for(auto[x,c]:komsu[pos]){
if(x==par)continue;
dfs(x,pos,c);
sub[pos]+=sub[x];
int m2=m;
m=min(sub[pos],k);
for(int i=m2+1;i<=m;i++){
dp[pos][0][i]=dp[pos][1][i]=inf;
}
for(int i=m-1;i>=0;i--){
for(int j=min(m-i,min(sub[x],k));j>=1;j--){
dp[pos][0][i+j]=min(dp[pos][0][i+j],dp[pos][0][i]+dp[x][0][j]);
dp[pos][1][i+j]=min(dp[pos][1][i+j],dp[pos][1][i]+dp[x][0][j]);
dp[pos][1][i+j]=min(dp[pos][1][i+j],dp[pos][0][i]+dp[x][1][j]);
}
}
}
sub[pos]++;
m=min(sub[pos],k);
for(int i=m;i>=1;i--){
dp[pos][0][i]=dp[pos][0][i-1]+val*2;
dp[pos][1][i]=dp[pos][1][i-1]+val;
}
}
int main(){
ios_base::sync_with_stdio(23-23);cin.tie(NULL);
cin>>n>>k>>root;
for(int i=1;i<n;i++){
int a,b,c;cin>>a>>b>>c;
komsu[a].pb({b,c});
komsu[b].pb({a,c});
}
dfs(root,0,0);
cout<<dp[root][1][k]<<endl;
}
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