#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;
}