func_code_string: #include <bits/stdc++.h>   using namespace std;   signed main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     long long n;     long double s;     cin >> n >> s;     vector<long long> cnt(n);     for (long long i = 0; i < n - 1; ++i) {       long long u, v;       cin >> u >> v;       --u;       --v;       ++cnt[u];       ++cnt[v];     }     long long ans = 0;     for (long long i = 0; i < n; ++i) ans += (cnt[i] == 1);     cout << setprecision(20) << 2.0 * s / ans << endl;     return 0;   }   