#include <bits/stdc++.h> #define ll long long using namespace std; const int mxN = 1e4+5; const ll INF = 1e18; vector <pair <int, ll>> adj[mxN]; vector <ll> dp[mxN][2]; vector <ll> mg(vector <ll> x, vector <ll> y, ll k) { vector <ll> z((int) x.size() + y.size() - 1, INF); for (int i = 0; i < x.size(); i++) for (int j = 0; j < y.size(); j++) z[i+j] = min(z[i+j], x[i] + y[j] + k*(j > 0)); return z; } void dfs(int u, int p) { dp[u][0] = dp[u][1] = {0, 0}; for (auto [v, w] : adj[u]) if (v != p) { dfs(v, u); dp[u][0] = mg(dp[u][0], dp[v][1], 2*w); dp[u][0] = mg(dp[u][1], dp[v][0], w); dp[u][1] = mg(dp[u][1], dp[v][1], 2*w); } for (int i = 0; i < dp[u][0].size(); i++) dp[u][0][i] = min(dp[u][0][i], dp[u][1][i]); } int main() { ios::sync_with_stdio(0), cin.tie(0); int n, k, x; cin >> n >> k >> x; for (int i = 1; i < n; i++) { int u, v; ll w; cin >> u >> v >> w; adj[u].emplace_back(v, w); adj[v].emplace_back(u, w); } dfs(x, x); cout << dp[x][0][k] << '\n'; }