def isqrt(n):
 if (n < 17984395633462800708566937239552L):
  return int(_sqrt(n))
 return integer_nthroot(int(n), 2)[0]

def isqrt ( n ) : if ( n < 17984395633462800708566937239552 L ) : return int ( _sqrt ( n ) ) return integer_nthroot ( int ( n ) , 2 ) [ 0 ]
return the largest integer less than or equal to sqrt(n) .