#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];
int main()
{
    int n,c=0,i;
    in>>n;
    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
            for (int j=i*2;j<=n;j+=i)
            {
                v[j]=1;
                c++;
            }
            out<<c;
    }

    return 0;
}