#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e4 + 2;
struct Node {
int v, w;
};
vector<Node> g[maxn];
int n, k, x;
int sz[maxn];
int memo[maxn][maxn][2];
void dfs(int x, int p) {
sz[x] = 1;
for (auto node : g[x]) {
if (node.v == p) continue;
dfs(node.v, x);
sz[x] += sz[node.v];
}
for (int i = 2; i <= min(sz[x], k); ++i) {
memo[x][i][0] = memo[x][i][1] = 1e9;
}
for (auto node : g[x]) {
if (node.v == p) continue;
for (int i = min(sz[x], k); i >= 2; --i) {
for (int j = 1; j <= min(sz[node.v], i-1); ++j) {
memo[x][i][1] = min(memo[x][i][1],
min(
memo[x][i-j][1] + memo[node.v][j][0] + 2*node.w,
memo[x][i-j][0] + memo[node.v][j][1] + node.w
));
memo[x][i][0] = min(memo[x][i][0],
memo[x][i-j][0] + memo[node.v][j][0] + 2*node.w);
}
}
}
}
int main() {
cin >> n >> k >> x;
for (int i = 1; i <= n-1; ++i) {
int a, b, c;
cin >> a >> b >> c;
g[a].push_back({b, c});
g[b].push_back({a, c});
}
dfs(x, 0);
cout << memo[x][k][1] << endl;
return 0;
}
