#include <bits/stdc++.h>   using namespace std;   int n, m;   int dmap[45][45];   int ans[45];   int dans[45];   int nans, zans;   void dfs(int dn) {     if (dn == n + 1) {       if (nans > zans) {         zans = nans;       }       return;     }     int mark = 0;     for (int i = 1; i < dn; i++)       if (ans[i] == 1 && dmap[i][dn] == 0) mark = 1;     if (mark == 0) {       ans[dn] = 1;       nans++;       dfs(dn + 1);       nans--;     }     if (nans + n - dn > zans) {       ans[dn] = 0;       dfs(dn + 1);     }     return;   }   int main() {     scanf( %d%d , &n, &m);     for (int i = 1; i <= n; i++)       for (int j = 1; j <= n; j++) scanf( %d , &dmap[i][j]);     nans = 0;     zans = 0;     dfs(1);     double zzans = zans;     printf( %lf n , (zzans - 1) / zzans / 2 * m * m);     return 0;   }   