#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll INF = (ll)4e18;
int n, K, X;
vector<pair<int,int>> g[100005];
int sz[100005];
struct NodeDP {
vector<ll> f0, f1;
};
NodeDP dfs(int u, int p) {
sz[u] = 1;
NodeDP cur;
cur.f0.assign(2, INF);
cur.f1.assign(2, INF);
cur.f0[1] = cur.f1[1] = 0;
int curSZ = 1;
for (auto [v, w] : g[u]) if (v != p) {
NodeDP ch = dfs(v, u);
int vsz = min(sz[v], K);
int newSZ = min(K, curSZ + vsz);
vector<ll> nf0(newSZ + 1, INF), nf1(newSZ + 1, INF);
for (int i = 1; i <= curSZ; ++i) {
if (cur.f0[i] >= INF && cur.f1[i] >= INF) continue;
for (int j = 1; j <= vsz && i + j <= newSZ; ++j) {
if (ch.f0[j] < INF) {
nf0[i + j] = min(nf0[i + j], cur.f1[i] + ch.f0[j] + w);
}
if (ch.f1[j] < INF) {
nf0[i + j] = min(nf0[i + j], cur.f0[i] + ch.f1[j] + 2LL*w);
nf1[i + j] = min(nf1[i + j], cur.f1[i] + ch.f1[j] + 2LL*w);
}
}
}
for (int i = 1; i <= curSZ; ++i) {
nf0[i] = min(nf0[i], cur.f0[i]);
nf1[i] = min(nf1[i], cur.f1[i]);
}
cur.f0.swap(nf0);
cur.f1.swap(nf1);
curSZ = newSZ;
sz[u] += sz[v];
}
int need = min(sz[u], K);
if ((int)cur.f0.size() > need + 1) cur.f0.resize(need + 1, INF);
if ((int)cur.f1.size() > need + 1) cur.f1.resize(need + 1, INF);
return cur;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> K >> X;
for (int i=1;i<n;++i){
int u,v,w; cin >> u >> v >> w;
g[u].push_back({v,w});
g[v].push_back({u,w});
}
NodeDP root = dfs(X, -1);
cout << root.f0[K] << "\n";
return 0;
}
