#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
// #define int long long
#define endl "\n"
//-------------------\\
constexpr int mod = 1e9 + 7, oo = 1e9, N = 10005;
vector<pair<int,int>> adj[N];
int sz[N];
int dp[N][N][2];
void calc(int u,int p) {
sz[u] = 1;
for (int i = 2;i < N; i++) dp[u][i][0] = dp[u][i][1] = oo;
for (auto [v,c] : adj[u]) {
if (v == p) continue;
calc(v,u);
for (int i = sz[u];i > 0; i--) {
for (int j = sz[v]; j > 0; j--) {
dp[u][i + j][0] = min(dp[u][i+j][0] , min(dp[u][i][1] + c + dp[v][j][0], dp[u][i][0] + 2*c + dp[v][j][1]));
dp[u][i + j][1] = min(dp[u][i+j][1] , dp[u][i][1] + 2*c + dp[v][j][1]);
}
}
sz[u] += sz[v];
}
}
void solve() {
int n,k,st; cin >> n >> k >> st;
for (int i = 1;i < n;i++) {
int u,v,c; cin >> u >> v >> c;
adj[u].push_back({v,c});
adj[v].push_back({u,c});
}
calc(st,-1);
cout << dp[st][k][0];
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cout << fixed << setprecision(9);
int t = 1;
// cin >> t;
while (t--) solve();
return 0;
}
