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

int p[1000001];

int main()
{
    int n, i, m = 0, j, nr = 0;

   f >>n;

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


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

   g<<nr<<'\n';


    return 0;
}