// Starcraft 2 enjoyer + luv kd //
#include <bits/stdc++.h>
using namespace std;
#define LSOne(X) ((X) & -(X))
const int N = 1e4 + 5;
const int M = 4e5 + 5;
const int S = 640;
const int O = 2e5 + 5;
const int K = 15;
const int LG = 21;
const int P = 37;
const long long INF = 1e18 + 5;
const int MOD = 1e9 + 7;
const int nx[] = {0, 1, 0, -1}, ny[] = {1, 0, -1, 0};
int n, k, st, sz[N];
vector<long long> dp1[N], dp2[N];
vector<pair<int, int>> adj[N];
void dfs(int c, int p)
{
sz[c] = 1;
dp1[c].push_back(0);
dp2[c].push_back(0);
dp1[c].push_back(INF);
dp2[c].push_back(INF);
for (auto &[i, w] : adj[c])
{
if (i == p)
continue;
dfs(i, c);
for(int x = 0; x < sz[i]; x++)
{
dp1[c].push_back(INF);
dp2[c].push_back(INF);
}
for (int x = sz[c]; x >= 0; x--)
{
for (int y = sz[i]; y >= 0; y--)
{
if (x + y <= k)
{
dp1[c][x + y] = min(dp1[c][x + y], dp1[c][x] + dp1[i][y] + 2*w);
dp2[c][x + y] = min(dp2[c][x + y], dp2[c][x] + dp1[i][y] + 2*w);
dp2[c][x + y] = min(dp2[c][x + y], dp1[c][x] + dp2[i][y] + w);
}
}
}
sz[c] += sz[i];
}
for (int x = sz[c]; x >= 1; x--)
{
dp1[c][x] = min(dp1[c][x - 1], dp1[c][x]);
dp2[c][x] = min(dp2[c][x - 1], dp2[c][x]);
}
}
void solve()
{
cin >> n >> k >> st;
for (int x = 0; x < n - 1; x++)
{
int a, b, c;
cin >> a >> b >> c;
adj[a].push_back({b, c});
adj[b].push_back({a, c});
}
dfs(st, 0);
cout << dp2[st][k];
}
signed main()
{
// freopen("CP.INP", "r", stdin);
// freopen("CP.OUT", "w", stdout);
// freopen("art2.in", "r", stdin);
// freopen("art2.out", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
for (int x = 1; x <= t; x++)
{
solve();
}
return 0;
}
