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

int p[1000001];

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

   f >>n;

    for(i = 3; i<= n; i+=2)
        if(p[i] == 0)
    {
        nr++;

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



   g<<nr<<'\n';

    return 0;
}