#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

bool V[2000001];
int main()
{
    int n, i, gg=0, j=0;
    in>>n;
    for (i=2; i<=n; i++)
    {
        if (V[i]==0)
        {
            gg++;
            for (j=i*2; j<=n; j+=i)
            {
                V[j]=1;
            }

        }
    }
    out<<gg;

    return 0;
}