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