#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

bitset <2000001> A ;

ifstream fin("ciur.in") ;
ofstream fout("ciur.out") ;

int main()
{
    int n ;
    fin >> n ;

    int cnt = 0 ;

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

    fout << cnt ;

    return 0;
}