#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
const int N = 10000;
const int INF = 0x3f3f3f3f;
int ij[N], ww[N], sz[N], dp[N][N + 1][2];
vector<int> eh[N];
int dfs(int h_, int i) {
int s_ = 1;
for (int h : eh[i])
if (h != h_) {
int j = i ^ ij[h], s = dfs(h, j);
for (int k = s_ + s; k; k--)
for (int f = 0; f < 2; f++)
if (k > s_)
dp[i][k][f] = INF;
else
for (int l = 1; l <= s; l++)
for (int g = 0; f + g < 2; g++)
dp[i][k + l][f + g] = min(dp[i][k + l][f + g], dp[i][k][f] + dp[j][l][g]);
s_ += s;
}
if (h_ != -1)
for (int k = 1; k <= s_; k++) {
dp[i][k][0] += ww[h_] * 2;
dp[i][k][1] += ww[h_];
}
return s_;
}
int main() {
ios_base::sync_with_stdio(false), cin.tie(NULL);
int n, k, r; cin >> n >> k >> r, r--;
for (int h = 0; h < n - 1; h++) {
int i, j, w; cin >> i >> j >> w, i--, j--;
ij[h] = i ^ j, ww[h] = w;
eh[i].push_back(h);
eh[j].push_back(h);
}
dfs(-1, r);
cout << dp[r][k][1] << '\n';
return 0;
}
