def inv2(A):
 n=len(A)
 Mx=[[F(x) for x in A[i]]+[F(1 if i==j else 0) for j in range(n)] for i in range(n)]
 for c in range(n):
  p=c
  while p<n and Mx[p][c]==0: p+=1
  if p==n: raise Exception('sing')
  Mx[c],Mx[p]=Mx[p],Mx[c]
  z=Mx[c][c]
  Mx[c]=[x/z for x in Mx[c]]