//#pragma GCC optimize("O3,unroll-loops,Ofast")
//#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
using namespace std;
// using namespace __gnu_pbds;
#define MAX 500005
#define pb push_back
// #define mp make_pair
// #define int long long
#define f first
#define s second
#define vi vector<int>
#define pii pair<int,int>
#define si set<int>
#define vpii vector<pair<int,int>>
const int mod = 1e9+7;
const int INF = 1e9;
// myMap.begin()->first : key
// myMap.begin()->second : value
int epow(int a,int b){int ans=1;while(b){if(b&1) ans*=a;a*=a;b>>=1;ans%=mod;a%=mod;}return ans%mod;}
int gcd(int a,int b) {if(a<b)swap(a,b);while(b){int tmp=b;b=a%b;a=tmp;}return a;}
int mul(int a,int b){return ((a%mod)*(b%mod))%mod;}
// int sum(int a,int b){return ((a%mod)+(b%mod))%mod;}
//typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
// typedef
// tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update>ordered_multiset;
vi sz(10003);
int dp[10003][10003][2];
vpii adj[10005];
void dfs(int node,int par){
sz[node]=1;
dp[node][1][1]=0;
for(auto u : adj[node]){
if(u.f==par) continue;
dfs(u.f,node);
for(int i=sz[node];i>=0;i--){
for(int j=0;j<=sz[u.f];j++){
dp[node][i+j][0]=min(dp[node][i+j][0],dp[node][i][1]+u.s+min(dp[u.f][j][0],dp[u.f][j][1]) );
dp[node][i+j][0]=min(dp[node][i+j][0],dp[u.f][j][1]+2*u.s+dp[node][i][0] );
dp[node][i+j][1]=min(dp[node][i+j][1], dp[node][i][1]+dp[u.f][j][1]+2*u.s );
}
}
sz[node]+=sz[u.f];
}
}
void solve(){
int n,k,x; cin>>n>>k>>x;
for(int i=0;i<=n;i++){
for(int j=0;j<=n;j++) dp[i][j][0]=dp[i][j][1]=INF;
}
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,0);
cout<<min(dp[x][k][0],dp[x][k][1])<<endl;
// for(int i=1;i<=7;i++) cout<<dp[3][i][0]<<" "<<dp[3][i][1]<<endl;
}
int32_t main(/*int32_t argc, char* argv[]*/){
std::ios_base::sync_with_stdio(0); std::cin.tie(0);
// freopen("disconnected.in", "r", stdin);
// freopen("disconnected.out", "w", stdout);
int t=1;
// cin >> t;
while (t--) solve();
return 0;
}
