#include <fstream>
using namespace std;
ifstream fi ( "ciur.in" );
ofstream fo ( "ciur.out" );
bool a[2000001];
int x, k, i, j;
int main()
{
    fi >> x;
    for ( i = 2 ; i <= x ; i++ )
        if ( a[i] == false )
        {
            for ( j = 2 ; j * i <= x ; j++ )
            a[i*j] = true;
            k++;
        }
    fo << k;
    return 0;
}