Can't find the actual problem in find greatest of three numbers python code

I am trying to find greatest number among three .

a = int(input('Enter number of a :- '))
b = int(input('Enter number of b :- '))
c = int(input('Enter number of c :- '))

if a>b or a>c :
    print(a)
elif b>a or b>c:
    print(b)
elif c>a or c>b:
    print(c)

It's working perfectly . But whenever I put the greatest number in c it doesn't work . It shows the greatest number among a and b .