#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define vi vector<int>
#define pb push_back
#define all(a) a.begin(),a.end()
const int mxn = 10001, inf = 1e9;
vector<pii> g[mxn];
vector<int> dp[mxn], dp2[mxn];
int sub[mxn];
int n,k,r;
void dfs(int u, int p){
sub[u] = 1;
dp[u].resize(2,0);
dp2[u].resize(2,0);
for(auto [v,c] : g[u]) if(v!=p){
dfs(v,u);
dp[u].resize(sub[u]+sub[v]+1,inf);
dp2[u].resize(sub[u]+sub[v]+1,inf);
for(int i = min(sub[u]+sub[v],k); i; i--)
for(int j = max(1,i-sub[v]); j <= min(i,sub[u]); j++){
dp[u][i] = min(dp[u][i],dp[u][j] + dp[v][i-j] + 2*c);
dp2[u][i] = min(dp2[u][i],dp[u][j] + dp2[v][i-j] + c);
dp2[u][i] = min(dp2[u][i],dp2[u][j] + dp[v][i-j] + 2*c);
}
sub[u] += sub[v];
}
}
void solve(){
cin >> n >> k >> r;
for(int i = 1; i < n; i++){
int u,v,c; cin >> u >> v >> c;
g[u].pb({v,c});
g[v].pb({u,c});
}
dfs(r,r);
cout << dp2[r][k];
}
signed main(){
cin.tie(0)->sync_with_stdio(0);
int t = 1;
// cin >> t;
while(t--){solve();}
}
