#include <bits/stdc++.h>
#define ll long long
#define all(aaa) aaa.begin(), aaa.end()
using namespace std;
struct E {
int to, w;
};
const int N = 1e4 + 5, K = N, INF = 1e9;
vector<E> g[N];
int dp[N][K][2], sz[N];
int n, k, x;
void upd(int &x, int y) {
x = min(x, y);
}
void dive(int node, int anc) {
sz[node] = 1;
for (E e : g[node]) {
if (e.to != anc) {
dive(e.to, node);
sz[node] += sz[e.to];
}
}
}
void dfs(int node, int h, int anc) {
dp[node][1][0] = dp[node][1][1] = 0;
int sum = 1;
for (E e : g[node]) {
if (e.to != anc) {
dfs(e.to, h + 1, node);
for (int x = min(sum, k - h); x > 0; x--) {
for (int y = 1; y <= min(sz[e.to], k - h - x); y++) {
upd(dp[node][x + y][0], dp[node][x][0] + dp[e.to][y][1] + e.w * 2);
upd(dp[node][x + y][0], dp[node][x][1] + dp[e.to][y][0] + e.w);
upd(dp[node][x + y][1], dp[node][x][1] + dp[e.to][y][1] + e.w * 2);
}
}
sum += sz[e.to];
}
}
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cin >> n >> k >> x;
x--;
for (int i = 0; i < n - 1; i++) {
int a, b, c;
cin >> a >> b >> c;
a--, b--;
g[a].push_back({b, c});
g[b].push_back({a, c});
}
for (int i = 0; i < N; i++) {
for (int j = 0; j < K; j++) {
for (int k = 0; k < 2; k++) {
dp[i][j][k] = INF;
}
}
}
dive(x, -1);
dfs(x, 0, -1);
cout << dp[x][k][0];
return 0;
}
