// https://oj.uz/problem/view/CEOI17_museum
#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int n, k, x; cin >> n >> k >> x;
vector<vector<pair<int, int>>> adj(n + 1);
for (int i=1, u, v, w; i<n; i++) {
cin >> u >> v >> w;
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
// dp[i][j][0] : the minimum cost to visit j nodes starting from node i
// dp[i][j][1] : the minimum cost to visit j nodes starting from node i and travel back to i
vector<vector<vector<int>>> dp(n + 1, vector<vector<int>>(n + 1, vector<int>(2, 0)));
vector<int> sz(n + 1, 0);
for (int i=1; i<=n; i++) {
for (int j=2; j<=n; j++) {
dp[i][j][0] = dp[i][j][1] = INF;
}
}
function<int(int, int)> findSize = [&] (int u, int p) -> int {
sz[u] = 1;
for (auto &[v, _] : adj[u]) {
if (v == p) continue;
sz[u] += findSize(v, u);
}
return sz[u];
};
findSize(x, 0);
function<void(int, int)> dfs = [&] (int u, int p) -> void {
int total = 1; // the total number of nodes can visit from node u
for (auto &[v, w] : adj[u]) {
if (v == p) continue;
dfs(v, u);
total += sz[v];
for (int i = total; i >= 2; i--) {
for (int j=0; j<=min(i, sz[v]); j++) {
// for (int j = max(0, i - total + sz[v]); j <= min(i, sz[v]); j++) { // take j nodes from v
// go v first, going back to -> go others, not going back to u
dp[u][i][0] = min(dp[u][i][0], dp[u][i-j][0] + dp[v][j][1] + 2 * w);
// go other first, go back to u -> go v, not not going back to u
dp[u][i][0] = min(dp[u][i][0], dp[u][i-j][1] + dp[v][j][0] + w);
// go other first, going back to u -> go v, going back to v
dp[u][i][1] = min(dp[u][i][1], dp[u][i-j][1] + dp[v][j][1] + 2 * w);
}
}
}
};
dfs(x, 0);
cout << dp[x][k][0] << "\n";
return 0;
}
