#include <bitset>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int N=2000000;
bitset<N+1> p;
int main()
{
    int n;
    in>>n;
    p.set();
    for (int i=2;i*i<=n;i++)
    {
        if (p[i])
        {
            for (int j=i*i;j<=n;j=j+i)
            {
                p[j]=false;
            }
        }
    }
    in.close();
    int nr=0;
    for (int i=2;i<=n;i++)
    {
        if (p[i])
            nr++;
    }
    out<<nr;
}