#include<bits/stdc++.h>
using namespace std;
const int N = 1e4 + 2;
std::vector<array<int, 2>> g[N];
const long long mx = 1LL << 60;
long long dp[2][N][N];
int dfs(int v, int par) {
int sz = 1;
for(auto &[u, w]:g[v]) {
if(u == par) continue;
int p = dfs(u, v);
for(int i = sz + 1; i <= sz + p; i++)
dp[0][v][i] = dp[1][v][i] = mx;
for(int i = sz + p; i >= 0; i--) {
for(int j = max(i - p, 0); j <= min(i, sz); j++) {
int k = i - j;
dp[0][v][i] = min(dp[0][v][i], dp[0][v][j] + dp[1][u][k] + w + w);
dp[0][v][i] = min(dp[0][v][i], dp[1][v][j] + dp[0][u][k] + w);
dp[1][v][i] = min(dp[1][v][i], dp[1][v][j] + dp[1][u][k] + w + w);
}
}
sz += p;
}
return sz;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
//cin >> t;
while(t--) {
int n, k, x; cin >> n >> k >> x;
for(int i = 1; i < n; i++) {
int a, b, c; cin >> a >> b >> c;
g[a].push_back({b, c});
g[b].push_back({a, c});
}
dfs(x, 0);
cout << min(dp[0][x][k], dp[1][x][k]) << "\n";
}
return 0;
}
