#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define rall(x) x.rbegin(), x.rend()
using namespace std;
using ll = long long;
constexpr long long inf = LLONG_MAX;
constexpr int mod = 1000000007;
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
for (size_t i = 0; i < v.size(); ++i) {
os << v[i];
if (i + 1 < v.size()) {
os << " ";
}
}
return os;
}
template<typename T>
istream& operator>>(istream& is, vector<T>& v) {
for (auto& x : v) {
is >> x;
}
return is;
}
void solve(){
int n, k, x; cin>>n>>k>>x;
vector<vector<pair<int, int>>> g(n+1);
for (int i = 0; i<n-1; i++){
int u, v, c; cin>>u>>v>>c;
g[u].push_back({v, c});
g[v].push_back({u, c});
}
vector<vector<vector<ll>>> dp(n+1);
vector<int> sz(n+1);
auto dfs = [&] (auto&& self, int u, int p) -> void {
sz[u] = 1;
for (auto [e, w]: g[u]){
if (e!=p){
self(self, e, u);
sz[u]+=sz[e];
}
}
dp[u].assign(sz[u]+1, vector<ll>(2, 1e18));
dp[u][1][0] = dp[u][1][1] = 0;
int L = min(k, sz[u]);
for (auto [e, w]: g[u]){
if (e!=p){
vector<vector<ll>> ndp = dp[u];
for (int i = 1; i<=L; i++){
for (int j = 1; j<=min(sz[e], L-i); j++){
ndp[i+j][0] = min(ndp[i+j][0], dp[e][j][0]+dp[u][i][1]+w);
ndp[i+j][0] = min(ndp[i+j][0], dp[e][j][1]+dp[u][i][0]+2*w);
ndp[i+j][1] = min(ndp[i+j][1], dp[e][j][1]+dp[u][i][1]+2*w);
}
}
swap(dp[u], ndp);
}
}
};
dfs(dfs, x, x);
cout<<dp[x][k][0];
}
int main() {
ios::sync_with_stdio(0); cin.tie(0);
int t = 1;
//cin>>t;
while(t--){
solve();
cout<<endl;
}
}
