#include<bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
//using namespace __gnu_pbds;
#define ll long long
#define smid (nl + nr) / 2
#define lc id * 2
#define rc id * 2 + 1
#define migmig std::ios_base::sync_with_stdio(false);std::cin.tie(NULL);std::cout.tie(NULL);
//template <class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
const int N = 1e4 + 5;
vector<int> dp[N][2];
vector<pair<int, int>> adj[N];
int sz[N];
int n, k, x;
int ans = 0;
void dfs (int v, int pre = 0) {
sz[v] = 1;
for (auto [u, c] : adj[v]) {
if (u == pre) continue;
dfs(u, v);
sz[v] += sz[u];
}
for (int i = 0; i <= min(sz[v], k); i++) {
dp[v][0].push_back(1e9);
dp[v][1].push_back(1e9);
}
dp[v][0][0] = 0;
dp[v][0][1] = 0;
dp[v][0][1] = 0;
dp[v][1][1] = 0;
for (auto [u, c] : adj[v]) {
if (u == pre) continue;
for (int j = min(k, sz[v]); j >= 0; j--) {
for (int l = min(k, sz[u]); l >= 0; l--) {
if (j >= l) dp[v][0][j] = min(dp[v][0][j], dp[u][0][l] + c + dp[v][1][j - l]);
if (j >= l) dp[v][0][j] = min(dp[v][0][j], dp[u][1][l] + c + c + dp[v][0][j - l]);
if (j >= l) dp[v][1][j] = min(dp[v][1][j], dp[u][1][l] + c + c + dp[v][1][j - l]);
}
}
}
for (auto [u, c] : adj[v]) {
if (u == pre) continue;
dp[u][0].clear();
dp[u][1].clear();
dp[u][0].shrink_to_fit();
dp[u][1].shrink_to_fit();
}
}
void solve() {
cin >> n >> k >> x;
for (int i = 1; i < n; i++) {
int a, b, c; cin >> a >> b >> c;
adj[a].push_back({ b, c });
adj[b].push_back({ a, c });
}
dfs(x);
cout << dp[x][0][k];
}
int main() {
migmig;
int T = 1;
//cin >> T;
while (T--) {
solve();
}
}
