#include <bits/stdc++.h>
using namespace std;
const int NMAX=1e4;
int dp[NMAX+5][NMAX+5][2], n, subtree[NMAX+5], k, x;
vector <pair <int, int>> vec[NMAX+5];
void dfs (int nod, int tatal=0)
{
subtree[nod]=1;
dp[nod][1][0]=dp[nod][1][1]=0;
for (auto adj : vec[nod])
{
if (adj.first==tatal)
continue;
dfs (adj.first, nod);
for (int i=min(k, subtree[nod]);i>=0;i--)
{
for (int j=min (k-i, subtree[adj.first]);j>=0;j--)
{
dp[nod][i+j][1]=min (dp[nod][i+j][1], dp[nod][i][1]+dp[adj.first][j][1]+adj.second*2);
dp[nod][i+j][0]=min (dp[nod][i+j][0], dp[nod][i][1]+dp[adj.first][j][0]+adj.second);
dp[nod][i+j][0]=min (dp[nod][i+j][0], dp[nod][i][0]+dp[adj.first][j][1]+adj.second*2);
}
}
subtree[nod]+=subtree[adj.first];
}
}
int main ()
{
memset (dp, 0x3f, sizeof (dp));
cin >> n >> k >> x;
for (int i=1;i<n;i++)
{
int x, y, w;
cin >> x >> y >> w;
vec[x].push_back ({y, w});
vec[y].push_back ({x, w});
}
dfs (x);
cout << min (dp[x][k][0], dp[x][k][1]);
return 0;
}
