def aliquot(n):
"""returns the aliquot of a number which
is defined as the sum of all the proper
divisors of a number"""
sum = 1
i = 2
while i * i < n:
if n % i == 0:
sum += i + (n / i)
i += 1
if i*i == n: sum += i
return sum
n = int(raw_input('Enter a number? '))
print aliquot(n)