#!/usr/bin/python2
# -*- coding: utf-8 -*-
# †
def sum_of_primes(n):
    r = int(n ** .5)
    V = [n//i for i in xrange(1, r+1)]
    V += reversed(xrange(V[-1]))
    S = {i: i*(i+1)//2-1 for i in V}
    for p in xrange(2, r+1):
        if S[p] > S[p-1]:
            p2 = p * p
            for v in V:
                if v < p2:
                    break
                S[v] -= p * (S[v//p] - S[p-1])
    return S[n]

n = int(raw_input())
print sum_of_primes(n)