n= int(input())
ans = [0] * (n+1)

for i in range(2,n+1):
	t = i+i
	while t <= n:
		ans[t] = 1 
		t += i
		
a = 0
for i in range(2,n+1):
	if ans[i] == 0:
		a+=i
print(a)