#include <fstream>
#define Nmax 2000001
using namespace std;

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

bool prim[ Nmax ];

int main()
{
    int nrp = 0, n;

    f >> n;

    for ( int i = 2; i <= n; ++ i )
    {
        if ( prim[ i ] == false )
        {
            nrp ++;
            for ( int j = i + i; j <= n; j += i )
                prim[ j ] = true;
        }
    }

    g << nrp;
    return 0;
}