#include <bits/stdc++.h>   using namespace std;   const int MAXN = 1e5;   int edges[MAXN] = {0};   int main() {     int n, s;     cin >> n >> s;     for (int i = 0; i < n - 1; i++) {       int a, b;       cin >> a >> b;       a--, b--;       edges[a]++, edges[b]++;     }     int amt = 0;     for (int i = 0; i < n; i++) {       if (edges[i] == 1) amt++;     }     double ans = ((double)s) / ((double)amt);     cout << fixed << setprecision(10) << ans * 2 << endl;   }   