input: Write a python function to compute the average of 5 numbers.
  assert average(1, 2, 3, 4, 5)==3.0
  assert average(10, 20, 30, 40, 50)==30.0
  assert average(5, 10, 15, 20, 25)==15.0
output: def average(a, b, c, d, e):
      return (a + b + c + d + e) / 5