/*
* Author: Nonoze
* Created: Saturday 03/01/2026
*/
#include <bits/stdc++.h>
using namespace std;
#ifndef DEBUG
#define dbg(...)
#endif
// #define cout cerr << "OUT: "
#define endl '\n'
#define endlfl '\n' << flush
#define quit(x) return (void)(cout << x << endl)
template<typename T> void read(T& x) { cin >> x; }
template<typename T1, typename T2> void read(pair<T1, T2>& p) { read(p.first), read(p.second); }
template<typename T> void read(vector<T>& v) { for (auto& x : v) read(x); }
template<typename T1, typename T2> void read(T1& x, T2& y) { read(x), read(y); }
template<typename T1, typename T2, typename T3> void read(T1& x, T2& y, T3& z) { read(x), read(y), read(z); }
template<typename T1, typename T2, typename T3, typename T4> void read(T1& x, T2& y, T3& z, T4& zz) { read(x), read(y), read(z), read(zz); }
template<typename T> void print(vector<T>& v) { for (auto& x : v) cout << x << ' '; cout << endl; }
#define sz(x) (int)(x.size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define make_unique(v) sort(all(v)), v.erase(unique(all(v)), (v).end())
#define pb push_back
#define mp(a, b) make_pair(a, b)
#define fi first
#define se second
#define cmin(a, b) a = min(a, b)
#define cmax(a, b) a = max(a, b)
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define QYES quit("YES")
#define QNO quit("NO")
// #define int long long
#define double long double
const int inf = numeric_limits<int>::max() / 4;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MOD = 1e9+7, LOG=20;
void solve();
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
int tt=1;
// cin >> tt;
while(tt--) solve();
return 0;
}
int n, k, m, q;
vector<vector<pair<int, int>>> adj;
pair<vector<int>, vector<int>> dfs(int u, int p=-1) {
vector<pair<vector<int>, vector<int>>> childs_ans;
for (auto [v, w] : adj[u]) if (v!=p) {
childs_ans.pb(dfs(v, u));
for (auto &x: childs_ans.back().fi) x+=w*2;
for (auto &x: childs_ans.back().se) x+=w;
childs_ans.back().fi.insert(childs_ans.back().fi.begin(), 0);
childs_ans.back().se.insert(childs_ans.back().se.begin(), 0);
}
if (childs_ans.empty()) return {{0}, {0}};
// first: comeback, second: goaway
sort(all(childs_ans), [](auto &a, auto &b) { return sz(a.fi)<sz(b.fi); });
vector<int> comeback, goaway; swap(comeback, childs_ans.back().fi), swap(goaway, childs_ans.back().se); childs_ans.pop_back();
for (auto &child: childs_ans) {
vector<int> new_comeback(sz(comeback) + sz(child.fi)-1, inf);
vector<int> new_goaway(sz(goaway) + sz(child.se)-1, inf);
for (int i=0; i<sz(comeback); i++) {
for (int j=0; j<sz(child.fi); j++) {
cmin(new_comeback[i+j], comeback[i] + child.fi[j]);
}
for (int j=0; j<sz(child.se); j++) {
cmin(new_goaway[i+j], comeback[i] + child.se[j]);
}
}
for (int i=0; i<sz(goaway); i++) {
for (int j=0; j<sz(child.fi); j++) {
cmin(new_goaway[i+j], goaway[i] + child.fi[j]);
}
}
swap(comeback, new_comeback);
swap(goaway, new_goaway);
}
return {comeback, goaway};
}
void solve() {
int root;
read(n, k, root); root--;
adj.assign(n, {});
for (int i=0; i<n-1; i++) {
int u, v, w; read(u, v, w); u--, v--;
adj[u].pb({v, w}), adj[v].pb({u, w});
}
auto res = dfs(root);
cout << res.se[k-1] << endl;
}
