#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif
const int N = 1e4;
int n, k, x;
int a[N][N + 1], b[N][N + 1];
vector<array<int, 2>> g[N];
int dfs(int u, int p) {
int x = 1;
a[u][1] = b[u][1] = 0;
for (auto [v, w] : g[u]) {
if (v ^ p) {
int y = dfs(v, u);
for (int i = x; i; --i) {
for (int j = y; j; --j) {
a[u][i + j] = min(a[u][i + j], a[u][i] + a[v][j] + 2 * w);
b[u][i + j] = min({b[u][i + j], a[u][i] + b[v][j] + w, b[u][i] + a[v][j] + 2 * w});
}
}
x += y;
}
}
return x;
}
int main() {
ios::sync_with_stdio(false); cin.tie(nullptr);
cin >> n >> k >> x; --x;
for (int i = 1; i < n; ++i) {
int u, v, c; cin >> u >> v >> c; --u, --v;
g[u].push_back({v, c});
g[v].push_back({u, c});
}
memset(a, 0x3f, sizeof(a));
memset(b, 0x3f, sizeof(b));
dfs(x, x);
cout << b[x][k];
return 0;
}
