#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e4 + 10;
int sub[MAXN];
int dp[MAXN][MAXN][2], min_dp[MAXN][MAXN];
vector<pair<int, int>> adj[MAXN];
int n, k, x;
void init(int v){
sub[v] = 1;
for(int i=0; i<=n; i++) dp[v][i][0] = dp[v][i][1] = 1e9;
dp[v][0][0] = dp[v][1][0] = 0;
dp[v][0][1] = dp[v][1][1] = 0;
}
void merge(int u, int w, int v){
for(int i=sub[v]; i>=0; i--){
for(int j=sub[u]; j>=0; j--){
dp[v][i + j][1] = min(dp[v][i + j][1], dp[v][i][1] + dp[u][j][1] + 2 * w);
dp[v][i + j][0] = min(dp[v][i + j][0], dp[v][i][0] + dp[u][j][1] + 2 * w);
dp[v][i + j][0] = min(dp[v][i + j][0], dp[v][i][1] + dp[u][j][0] + w);
}
}
sub[v] += sub[u];
}
void dfs(int v, int p){
init(v);
for(auto [u, w] : adj[v]){
if(u != p){
dfs(u, v);
merge(u, w, v);
}
}
}
int main(){
cin.tie(0)->sync_with_stdio(0);
cin >> n >> k >> x;
for(int i=1; i<n; i++){
int a, b, c; cin >> a >> b >> c;
adj[a].push_back({b, c});
adj[b].push_back({a, c});
}
dfs(x, x);
cout << dp[x][k][0] << "\n";
return 0;
}
