#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define mp make_pair
#define pb push_back
#define x first
#define y second
#define pii pair<int, int>
#define p3i pair<pii, int>
#define pll pair<ll, ll>
#define p3l pair<pll, ll>
#define lseg L, (L+R)/2, N*2+1
#define rseg (L+R)/2+1, R, N*2+2
#define ub upper_bound
#define lb lower_bound
#define pq priority_queue
#define MN 1000000007
#define fox(k, x) for (int k=0; k<x; ++k)
#define fox1(k, x) for (int k=1; k<=x; ++k)
#define foxr(k, x) for (int k=x-1; k>=0; --k)
#define fox1r(k, x) for (int k=x; k>0; --k)
#define ms multiset
#define flood(x) memset(x, 0x3f3f3f3f, sizeof x)
#define drain(x) memset(x, 0, sizeof x)
#define rng() (rand() >> 3)*rand()
int n, k, x, a, b, d, hi[10005], dp[2][10005][10005];
vector<pii> v[10005];
void dfs(int N, int P){
dp[0][N][1]=dp[1][N][1]=0;
hi[N]=1;
int c;
fox(l, v[N].size()){
c=v[N][l].x;
if (c==P) continue;
dfs(c, N);
fox1r(l2, hi[N]){
fox1(l3, hi[c]){
dp[0][N][l2+l3]=min(dp[0][N][l2+l3], dp[0][N][l2]+dp[0][c][l3]+v[N][l].y*2);
dp[1][N][l2+l3]=min(dp[1][N][l2+l3], dp[1][N][l2]+dp[0][c][l3]+v[N][l].y*2);
dp[1][N][l2+l3]=min(dp[1][N][l2+l3], dp[0][N][l2]+dp[1][c][l3]+v[N][l].y);
}
}
hi[N]+=hi[c];
}
/*cout << N<< ' ' << hi[N] << endl;
fox1(l, hi[N]){
cout << dp[0][N][l] << ' ';
} cout << endl;*/
}
int main(){
flood(dp);
cin >> n >> k >> x;
fox(l, n-1){
cin >> a >> b >> d;
v[a].pb(mp(b, d));
v[b].pb(mp(a, d));
}
dfs(x, -1);
cout << dp[1][x][k];
return 0;
}
