#Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
#If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called amicable numbers.

#For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.

#Evaluate the sum of all the amicable numbers under 10000.
#Project Euler #21: Amicable numbers

Limit = int(input("Limit?"))
ds = [1]*Limit
for i in range(2, int(Limit**0.5)):
	for a in range(i+1, Limit//i):
		ds[i*a]+= i+a

an = []
for i in range(2, Limit):
	if ds[i] < i and ds[ds[i]] == i: an+= [ds[i], i]


print("Amicable sum <",Limit,"=", sum(a for a in an if a<Limit))