#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char c[2000001];
int main()
{
    int n, nr, p, m, i;
    f >> n;
    /*for(p = 2; p * p <= n; p++)
        if(c[p] == 0)
            for( m = p * p; m <= n; m += p)
                c[m] = 1;
    nr = 0;
    for( i = 2; i <= n; i++ )
        if( c[i] == 0 )
            nr++;
    g << nr;*/

    nr = n - 1;
    for(p = 2; p * p <= n; p++)
        if(c[p] == 0)
            for( m = p * p; m <= n; m += p){
                    nr--;
                    c[m] = 1;
            }
    g << nr;


    return 0;
}