#include <bits/stdc++.h>
using namespace std;
const int MAXN = 505;
const int MAXK = 505;
#define int long long
const int INF = 5e18;
vector<pair<int, int>> adj[MAXN];
int dp[MAXN][MAXK][2];
int n, k, x;
void dfs(int u, int par) {
dp[u][1][0] = 0;
dp[u][1][1] = 0;
for (auto [v, cost] : adj[u]) {
if (v == par) continue;
dfs(v, u);
int tmp[MAXK][2];
for (int i = 0; i <= k; ++i) tmp[i][0] = tmp[i][1] = INF;
for (int i = 1; i <= k; ++i) {
if (dp[u][i][0] == INF && dp[u][i][1] == INF) continue;
for (int j = 1; j <= k - i; ++j) {
if (dp[v][j][0] == INF && dp[v][j][1] == INF) continue;
tmp[i + j][0] = min(tmp[i + j][0], dp[u][i][0] + dp[v][j][0] + 2 * cost);
tmp[i + j][1] = min(tmp[i + j][1], dp[u][i][0] + dp[v][j][1] + cost);
tmp[i + j][1] = min(tmp[i + j][1], dp[u][i][1] + dp[v][j][0] + 2 * cost);
}
}
for (int i = 2; i <= k; ++i) {
dp[u][i][0] = min(dp[u][i][0], tmp[i][0]);
dp[u][i][1] = min(dp[u][i][1], tmp[i][1]);
}
}
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> x >> k;
for (int i = 1; i < n; ++i) {
int a, b, c;
cin >> a >> b >> c;
adj[a].emplace_back(b, c);
adj[b].emplace_back(a, c);
}
for (int i = 1; i <= n; ++i)
for (int j = 0; j <= k; ++j)
dp[i][j][0] = dp[i][j][1] = INF;
dfs(x, -1);
int answer = min(dp[x][k][0], dp[x][k][1]);
cout << answer << '\n';
return 0;
}
