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