import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

n = I()
p = [2]
for i in range(3, n+1):
    for j in range(2, int(i**0.5)+2):
        if i%j == 0:
            break
    else:
        p.append(i)

if n == 1:
    print(0)
else:
    print(sum(p))