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