#include <fstream>

using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");

bool v[1000000];

int main()
{
    int n,i,z,gigi=0;
    in>>n;
    v[0]=1;
    v[1]=1;
    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
        {
            for (z=i+i;z<=n;z+=i)
            {
                v[z]=1;
            }
            gigi++;
        }
    }
    out<<gigi;
    return 0;
}