func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 200005;   vector<int> g[N];   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     int n, s;     cin >> n >> s;     for (int i = 0; i < n - 1; ++i) {       int a, b;       cin >> a >> b;       g[a].push_back(b);       g[b].push_back(a);     }     int leaves = 0;     for (int i = 1; i <= n; ++i) {       if (g[i].size() == 1) leaves++;     }     long double ans = (long double)(2 * s) / (long double)leaves;     cout << fixed << setprecision(8) << ans << endl;     return 0;   }   