#include<bits/stdc++.h>
using namespace std;
const int N = 10005;
struct Edges{
int x, c;
};
vector<Edges> gr[N];
int sz[N];
void dfs_prec(int nod, int dad){
sz[nod] = 1;
for(auto x:gr[nod])
if(x.x!=dad){
dfs_prec(x.x, nod);
sz[nod] += sz[x.x];
}
}
int dp[2][N][N];
void joindp(int dp1[], int sz1, int dp2[], int sz2, int dpans[], int val){
for(int i = sz1; i >=0; i--){
for(int j = sz2; j>=0; j--){
dpans[i + j] = min(dpans[i + j], dp1[i] + dp2[j] + val);
}
}
}
void dfs(int nod, int dad){
for(auto x:gr[nod]){
if(x.x != dad){
dfs(x.x, nod);
}
}
dp[0][nod][0] = 0;
dp[1][nod][0] = 0;
dp[0][nod][1] = 0;
dp[1][nod][1] = 0;
int cursz = 1;
for(auto x:gr[nod]){
if(x.x == dad)
continue;
joindp(dp[1][nod], cursz, dp[0][x.x], sz[x.x], dp[1][nod], 2*x.c);
joindp(dp[0][nod], cursz, dp[1][x.x], sz[x.x], dp[1][nod], x.c);
joindp(dp[0][nod], cursz, dp[0][x.x], sz[x.x], dp[0][nod], 2*x.c);
cursz+=sz[x.x];
}
}
int main()
{
//freopen(".in","r",stdin);
ios::sync_with_stdio(false);
cin.tie(0),cout.tie(0);
for(int i = 0; i < 2; i++){
for(int j = 0; j < N; j++){
for(int k = 0; k < N; k++){
dp[i][j][k] = INT_MAX;
}
}
}
int n, k, x;
cin>>n>>k>>x;
for(int i =1; i < n; i++){
int a, b, c;
cin>>a>>b>>c;
gr[a].push_back({b, c});
gr[b].push_back({a, c});
}
dfs_prec(x, 0);
dfs(x, 0);
cout<<dp[1][x][k];
return 0;
}
