#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n , nr;

bool v[2000005];

int main()
{
    f >> n ;

    nr = 1;

    for ( int i = 3 ; i <= n ; i = i + 2)
    {
        if(v[i] == 0)
        {
            nr++;
            for (int j = i + i ; j <= n ; j = j + i)
                v[j] = 1;
        }
    }

    g << nr ;

    return 0;
}