input: Write a python function to check if a number is a perfect square.
  assert is_perfect_square(16) == True
  assert is_perfect_square(25) == True
  assert is_perfect_square(26) == False
  assert is_perfect_square(0) == True
  assert is_perfect_square(-4) == False
output: def is_perfect_square(n):
      if n < 0:
          return False
      root = int(n**0.5)
      return root * root == n