// https://oj.uz/problem/view/CEOI17_museum
#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
const int MAXN = 1e4 + 5;
int dp[MAXN][MAXN][2];
int sz[MAXN];
vector<pair<int, int>> adj[MAXN];
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int n, k, x; cin >> n >> k >> x;
// dp[i][j][0]: minimum cost to take j nodes starting from node i,
// dp[i][j][1]: minimum cost to take j nodes starting from node i, going back to its parent
for (int i=1; i<=n; i++) {
for (int j=2; j<=n; j++) {
dp[i][j][0] = dp[i][j][1] = INF;
}
}
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});
}
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;
for (auto &[v, w] : adj[u]) {
if (v == p) continue;
dfs(v, u);
for (int i=total; i>=0; i--) {
for (int j=0; j<=sz[v]; j++) {
// going others first, going back -> go to v, not going back
dp[u][i + j][0] = min(dp[u][i + j][0], dp[u][i][1] + dp[v][j][0] + w);
// going to v first, going back -> going to others, not going back
dp[u][i + j][0] = min(dp[u][i + j][0], dp[u][i][0] + dp[v][j][1] + 2 * w);
// going to v and others, and go back
dp[u][i + j][1] = min(dp[u][i + j][1], dp[u][i][1] + dp[v][j][1] + 2 * w);
}
}
total += sz[v];
}
};
dfs(x, 0);
cout << dp[x][k][0] << "\n";
return 0;
}
