#include<bits/stdc++.h>
#include <sys/_types/_size_t.h>
using namespace std;
#define int long long
#define F first
#define S second
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define pb push_back
#define sz(x) (int)(x.size())
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
#define vi vector<int>
#define vp vector<pii>
#define vvi vector<vi>
#define ykh mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count())
#define __lg(x) 63-__builtin_clzll(x)
#define pow2(x) (1LL<<x)
void __print(int x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef local
void setio(){freopen("/Users/iantsai/Library/Mobile Documents/com~apple~CloudDocs/cpp/Empty.md","r",stdin);}
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
void setio(){}
#define debug(x...)
#endif
void setIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
struct line{
int a,b;
int operator()(const int x)const{
return a*x+b;
}
};
bool check(line l1,line l2,line l3){
return (l3.b-l2.b)*(l1.a-l2.a)<=(l2.b-l1.b)*(l2.a-l3.a);
}
const int mxn=1e4+5;
vector<pii>adj[mxn];
vector<vector<vector<int>>>dp(mxn,vector<vector<int>>(2));
int cnt[mxn];
void dfs(int v,int pa){
cnt[v]=1;
dp[v][0].pb(0);//停在v
dp[v][0].pb(0);
dp[v][1].pb(0);
dp[v][1].pb(0);//停在任一點
for(auto [u,d]:adj[v]){
if(u==pa)continue;
dfs(u,v);
vector<vector<int>>temp(2,vector<int>(cnt[v]+cnt[u]+1,1e9));
for(int i=0;i<=cnt[v];i++){
for(int j=0;j<=cnt[u];j++){
chmin(temp[0][i+j],dp[v][0][i]+dp[u][0][j]+d*2*(j>0));
chmin(temp[1][i+j],dp[v][0][i]+dp[u][1][j]+d);
chmin(temp[1][i+j],dp[v][1][i]+dp[u][0][j]+d*2*(j>0));
}
}
cnt[v]+=cnt[u];
dp[v]=temp;
}
}
signed main(){
setio();
ios::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int n,k,x;
cin>>n>>k>>x;
for(int i=1;i<n;i++){
int a,b,c;
cin>>a>>b>>c;
adj[a].pb({b,c});
adj[b].pb({a,c});
}
dfs(x,x);
cout<<dp[x][1][k]<<'\n';
/*for(int i=1;i<=n;i++){
for(int j=0;j<=cnt[i];j++){
//cout<<dp[i][0][j]<<','<<dp[i][1][j]<<' ';
}
//cout<<'\n';
}*/
}
/*
input:
*/
Compilation message
museum.cpp:2:10: fatal error: sys/_types/_size_t.h: No such file or directory
2 | #include <sys/_types/_size_t.h>
| ^~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
