#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn = 1e4 + 5;
vector<pair<int, int>> adj[maxn];
int sz[maxn], sum[maxn], n, k, x;
void minimize(int &a, int b){
a = min(a, b);
}
vector<array<int, 2>> dfs(int u, int p) {
sz[u] = 1;
vector<array<int, 2>> dp(n + 1, array<int, 2>{10000000000, 10000000000});
dp[1][0] = dp[0][0] = 0;
dp[1][1] = -sum[u];
for(auto [v, w]: adj[u]){
if(v == p) continue;
sum[v] = sum[u] + w;
vector<array<int, 2>> ndp = 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[i + j][0], dp[i][0] + ndp[j][0] + add);
minimize(dp[i + j][1], min(dp[i][0] + ndp[j][1], dp[i][1] + ndp[j][0]) + add);
}
}
sz[u] += sz[v];
}
dp.resize(sz[u] + 1);
return dp;
}
void solve(){
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});
}
cout << dfs(x, 0)[k][1];
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
solve();
}
