#include <bits/stdc++.h>   using namespace std;   int n;   double s;   vector<int> E[100005];   int dist[100005], pa[100005];   int dfs(int u, int p, int d) {     dist[u] = d;     int ans = u;     for (int v : E[u]) {       if (v == p) continue;       int tmp = dfs(v, u, d + 1);       pa[v] = u;       if (dist[ans] < dist[tmp]) ans = tmp;     }     return ans;   }   int main() {     scanf( %d%lf , &n, &s);     for (int i = 0; i < n - 1; i++) {       int u, v;       scanf( %d%d , &u, &v);       E[u].push_back(v);       E[v].push_back(u);     }     if (n == 2) {       printf( %.10lf n , s);       return 0;     }     int l = 0;     for (int i = 1; i <= n; i++) {       if (E[i].size() == 1) l++;     }     printf( %.10lf n , 2.0 * s / l);     return 0;   }   