n = int(input("n = "))
if n<0:
    print("Error: Not Defined!")
elif n==0:
    print("0! = 1")
else:
    f = 1
    for i in range(1,n+1):
        f *= i
    print(n, "! = ", f)

    ====================== RESTART: C:\n!.py ======================
    n = 0
    0! = 1
>>>
    ====================== RESTART: C:\n!.py ======================
    n = 1
    1 ! =  1
>>>
    ====================== RESTART: C:\n!.py ======================
    n = 6
    6 ! =  720
>>>
    ====================== RESTART: C:\n!.py ======================
    n = 10
    10 ! =  3628800
>>>
    ====================== RESTART: C:\n!.py ======================
    n = 17
    17 ! =  355687428096000
>>>
    ====================== RESTART: C:\n!.py ======================
    n = 50
    50 ! =  30414093201713378043612608166064768844377641568960512000000000000
>>>
    ====================== RESTART: C:\n!.py ======================
    n = -5
    Error: Not Defined!
>>>