#include <iostream>
#include <bitset>
#include <stdio.h>

using namespace std ;

const int NMAX = 2000005 ;
bitset <NMAX> use ;
int N, cnt ;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    cin >> N ;

    for(int i = 2 ; i <= N ; ++ i)
        if(use[i] == 0)
    {
        cnt ++ ;
        for(int j = i + i ; j <= N ; j = j + i)
            use[j] = 1 ;
    }

    cout << cnt << '\n' ;
    return 0 ;
}