Recursion problem : operating( 5!=1*2*3*4*5 etc....)

Question

I tried to input 3, and it would be perfect if it stoped here(picture below), but it kept running for two more steps and turned out outputting 3

a=1
k=0
def factorial(num):
    
    global a
    if num !=k:
        
        a=a*num
        factorial(num-1)
    else:
        return a
        

factorial(int(input()))    

enter image description here