#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn = 5e3 + 5;
vector<pair<int, int>> adj[maxn];
int sz[maxn], sum[maxn];
int dp[maxn][maxn][2];
void minimize(int &a, int b){
a = min(a, b);
}
void dfs(int u, int p) {
sz[u] = 1;
dp[u][1][0] = dp[u][0][0] = 0;
dp[u][1][1] = -sum[u];
for (auto [v, w]: adj[u]) {
if (v == p) continue;
sum[v] = sum[u] + w;
dfs(v, u);
for (int i = sz[u]; i >= 0; i--){
for (int j = 0; j <= sz[v]; j++) {
int add = 2 * w * (j > 0);
minimize(dp[u][i + j][0], dp[u][i][0] + dp[v][j][0] + add);
minimize(dp[u][i + j][1], min(dp[u][i][0] + dp[v][j][1], dp[u][i][1] + dp[v][j][0]) + add);
}
}
sz[u] += sz[v];
}
}
void solve(){
int n, k, x; cin >> n >> k >> x;
for (int i = 1; i <= n - 1; i++){
int u, v, w; cin >> u >> v >> w;
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
memset(dp, 0x3f, sizeof(dp));
dfs(x, 0);
cout << dp[x][k][1] << '\n';
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
solve();
}
