FactorialWrite a python function to find the factorial of given numberConstraints:4 < n < 20print -1 otherwiseInput format :Integer valueOutput format :Integer value

Sure, here is a Python function that calculates the factorial of a given number within the constraints you provided:

def factorial(n):
    # Check if the number is within the constraints
    if n < 4 or n > 20:
        return -1
    else:
        # Initialize the factorial to 1
        fact = 1
        # Calculate the factorial
        for i in range(1, n + 1):
            fact *= i
        return fact

You can use this function like this:

print(factorial(5))  # Output: 120
print(factorial(21))  # Output: -1

This function first checks if the input number n is within the constraints (4 < n < 20). If it's not, the function returns -1. If it is, the function calculates the factorial by initializing a variable fact to 1 and then multiplying it by every number from 1 to n in a loop. The result is then returned.