#include <bits/stdc++.h>
using namespace std;
const int mxN = 1e4 + 5;
const int INF = 1e9;
int dp[mxN][mxN][2], sz[mxN];
vector<pair<int, int>> adj[mxN];
void dfs(int u = 1, int par = -1){
dp[u][1][0] = dp[u][1][1] = 0;
sz[u] = 1;
for(auto [v, c] : adj[u]){
if(v ^ par){
dfs(v, u);
for(int i = sz[u]; i >= 1; --i){
for(int j = sz[v]; j >= 1; --j){
dp[u][i + j][0] = min(dp[u][i + j][0], dp[u][i][0] + dp[v][j][0] + 2 * c);
dp[u][i + j][1] = min(dp[u][i + j][1], dp[u][i][1] + dp[v][j][0] + 2 * c);
dp[u][i + j][1] = min(dp[u][i + j][1], dp[u][i][0] + dp[v][j][1] + c);
}
}
sz[u] += sz[v];
}
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(nullptr); cout.tie(nullptr);
int n, k, x, u, v, c;
cin >> n >> k >> x;
for(int i = 1; i <= n - 1; ++i){
cin >> u >> v >> c;
adj[u].push_back({v, c});
adj[v].push_back({u, c});
}
for(int i = 1; i <= n; ++i) for(int j = 0; j <= k; ++j) dp[i][j][0] = dp[i][j][1] = INF;
dfs(x, -1);
cout << min(dp[x][k][0], dp[x][k][1]) << "\n";
return 0;
}
