input: 
  def objective_function(a: int, b: int, c: int) -> int:
      """ Calculate the objective function of a linear equation ax + by = c.
      >>> objective_function(3, 5, 7)
      0
      >>> objective_function(2, -1, 4)
      2
      """
      return c
  
output:     if a == 0 and b == 0:
          return 0
      elif a == 0:
          return abs(c % b)
      elif b == 0:
          return abs(c % a)
      else:
          return abs(c % (a * b))