input: Write a function to calculate the factorial of a given number n. The function should return the factorial value.
  def factorial(n):
   fact = 1
   for i in range(2,n+1):
    fact = fact * i
   return fact
  
  assert factorial(7)==5040
  assert factorial(0)==1
  assert factorial(1)==1
  assert factorial(5)==120
  assert factorial(3)==6
output: def factorial(n):
   fact = 1
   for i in range(2,n+1):
    fact = fact * i
   return fact