from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline




N = int(input())
flg = [False]*(N+1)
ans = 0
if N==1:
    print(0)
    exit()

for i in range(2,N+1):

    if flg[i]:
        continue
    ans += i
    for j in range(i,N+1,i):
        flg[j] = True
print(ans)