#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define endl "\n"
#define vec vector<ll>
#define vecvec vector<vector<ll>>
using namespace std;
/*#define FileName ""
string Ghhhh = ".in";
string Ghhhhh = ".out";
ifstream Girdi(FileName + Ghhhh);
ofstream Cikti(FileName + Ghhhhh);
#define cin Girdi
#define cout Cikti*/
const ll INF = 1e15;
ll n,k,x;
vector<vector<ll>> adj;
vector<vector<ll>> dp;
map<pair<ll,ll>,ll> mapp;
vector<bool> vis;
inline vector<ll> total_min(vector<ll> a, vector<ll> b, ll cost){
vector<ll> combined(a.size() + b.size() - 1,INF);
combined[0] = 0;
for(ll i = 1 ; i < a.size() ; i++){
for(ll j = 0 ; j < b.size() ; j++){
if(j == 0){
combined[i+j] = min(combined[i+j],a[i] + b[j]);
}else{
combined[i+j] = min(combined[i+j],min(a[i] + 2 * (b[j] + cost), 2 * a[i] + b[j] + cost));
}
}
}
return combined;
}
inline void process(ll room){
vis[room] = 1;
dp[room] = {0,0};
for(auto go : adj[room]){
if(vis[go]) continue;
ll cost;
if(go > room){
swap(go,room);
cost = mapp[{go,room}];
swap(go,room);
}else cost = mapp[{go,room}];
process(go);
dp[room] = total_min(dp[room],dp[go],cost);
}
}
inline void solve(){
cin >> n >> k >> x;
adj.resize(n+1);
dp.resize(n+1);
vis.resize(n+1,0);
for(ll i = 1 ; i < n ; i++){
ll a,b,w;
cin >> a >> b >> w;
adj[a].pb(b);
adj[b].pb(a);
if(a > b) swap(a,b);
mapp[{a,b}] = w;
}
process(x);
cout << dp[x][k] << endl;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
ll t = 1;
//cin >> t;
while(t--){
solve();
}
}
