#include <fstream>

using namespace std;

bool prim[2000005], nr;

int main()
{
    ifstream in ("ciur.in");
    ofstream out ("ciur.out");
    int i, j, n;
    in>>n;
    for (i=2; i<=n; i++)
        prim[i]=1;
    for (i=2; i<=n; i++)
        if (prim[i])
        {
            nr++;
            for (j=i*i; j<=n; j+=i)
                prim[j]=0;
        }
    out<<nr;
    return 0;
}