#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,v[2000000+3],k;
int main()
{
    f>>n;
    for(int i=3;i<=n;i+=2)
    {
        if(!v[i])
        {
            k++;
            int j=2;


            while(i*j<=n)
            {
                v[i*j]=1;
                ++j;
            }
        }
    }
    g<<k;
    return 0;
}