#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#include <string.h>
using namespace std;
#define endl '\n'
#define ll long long
#define pi pair<int, int>
#define f first
#define s second
const int inf = 0x3f3f3f3f;
const int mxn = 10001;
int n, k, x;
int dp[mxn][mxn][2];
vector<pi> g[mxn];
void dfs(int c, int p){
memset(dp[c], inf, sizeof(dp[c]));
dp[c][1][0] = dp[c][1][1] = 0;
for(pi i : g[c]){
if(i.f == p) continue;
dfs(i.f, c);
for(int j = k; ~j; j--){
int ret[2] = {inf, inf};
for(int l = 0; l <= j; l++){
ret[0] = min(ret[0], dp[c][j - l][0] + dp[i.f][l][0] + 2 * i.s);
ret[1] = min(ret[1], dp[c][j - l][1] + dp[i.f][l][0] + 2 * i.s);
ret[1] = min(ret[1], dp[c][j - l][0] + dp[i.f][l][1] + i.s);
}
for(int l = 0; l < 2; l++){
dp[c][j][l] = min(dp[c][j][l], ret[l]);
}
}
}
}
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k >> x;
x--;
for(int i = 0; i < n - 1; i++){
int u, v, w;
cin >> u >> v >> w;
u--, v--;
g[u].push_back({v, w});
g[v].push_back({u, w});
}
dfs(x, -1);
cout << dp[x][k][1] << endl;
return 0;
}
