#include <bits/stdc++.h>   using namespace std;   vector<int> g[100005];   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int n, k, x, y;     cin >> n >> k;     for (int i = 0; i < n - 1; ++i) {       cin >> x >> y;       g[x].push_back(y);       g[y].push_back(x);     }     int kol = 0;     for (int i = 1; i <= n; ++i) {       if ((int)g[i].size() == 1) kol++;     }     cout << fixed << setprecision(7) << k / (double)(kol)*2 <<   n ;     return 0;   }   