#include <fstream>
#include <math.h>

using namespace std;

bool prim[2000007];

int main()
{
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    int n , nr = 0 ;
    cin>>n;
    for ( int i = 2 ; i <= sqrt(n) ; ++i )
        if ( prim [ i ] == 0 )
        for ( int j = i*i ; j <= n ; j = j+i )
            prim [ j ] = 1 ;
    for ( int i = 2 ; i <= n ; ++i )
        if ( prim [ i ] ==  0 ) nr++ ;
    cout<<nr;
    return 0;
}