number = []
for i in range(2, 1001):
	number.append(i)
prime = []
while number != []:
	newnumber = []
	prime.append(number.pop(0))
	while number != []:
		n = number.pop(0)
		if n % prime[-1] != 0: newnumber.append(n)
	number = newnumber
N = int(raw_input())
sum = 0
for i in range(0, len(prime)):
	if prime[i] > N: break
	sum += prime[i]
print sum