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

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

int n, nr;
bool v[ Nmax ];

int main()
{
    f >> n;

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