#include <fstream>
#include <cmath>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int p[2000001];

int main()
{
    long n, i, j, nr = 1;

   f >>n;

   for(i = 1; i <= n; i++)
    p[i] = 1;


    for(i = 3; i<= n; i+=2)
        if(p[i] == 1)
    {
        nr++;

        for(j =i+i+i; j <= n; j +=2*i)
            p[j] = 0;
    }



   g<<nr<<'\n';

    return 0;
}