How to turn back top of code after if statement

I've problem with, after if-statement limitation, code should follow user input again to take valid number. I just learned that using of try, except ValueError usage and couldn't fit it correctly i guess.

def factorial(num):
fact=1
for i in range(1,num+1):
    fact*=i
print(num,"! =",fact)


while True:
try:
    user_input=int(input("Give me a number:"))
    if user_input <= 0:
        print("Number should be greater than zero!")
except ValueError:
    print("Invalid Character!")
else:
    factorial(user_input)

-Actual result-

Give me a number:0
Number should be greater than zero!
0 ! = 1

0 ! = 1 calculation of fuctorial shouldn't be there. How can I fix this?