i = int(input(': '))
h = ''
while i > 0:
    q = str(i % 16)
    
    if q == '10':
        h = h + 'A'
        
    elif q == '11':
        h = h + 'B'
        
    elif q == '12':
        h = h + 'C'
        
    elif q == '13':
        h = h + 'D'
        
    elif q == '14':
        h = h + 'E'
        
    elif q == '15':
        h = h + 'F'
        
    else:
        h = h + q
               
        
    i = int(i / 16)
    
print(h[::-1])

>>> def tohex(n):
...     alpha = '0123456789ABCDEF'
...     out = '' if n else '0'
...     while n > 0:
...         out = alpha[n % 16] + out
...         n >>= 4
...     return out
... 
>>> print(tohex(0))
0
>>> print(tohex(1))
1
>>> print(tohex(15))
F
>>> print(tohex(16))
10
>>> print(tohex(255))
FF
>>> print(tohex(256))
100
>>>