input: Write a function to compute the factorial of a given integer. The function should return 1 if the integer is less than or equal to 1, otherwise it should recursively compute the factorial by multiplying the integer by the factorial of the integer minus one. Then prompt the user to input an integer, calculate its factorial using the defined function, and print the result.
  
  assert factorial(5)==120
  assert factorial(0)==1
  assert factorial(1)==1
  assert factorial(3)==6
  assert factorial(10)==3628800
output: def factorial(n):
      if n <= 1:
          return 1
      else:
          return n * factorial(n - 1)