#include <fstream>

using namespace std;

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

bool a[2000001];

int main()
{
    int i,j,nr=0,n;
    in>>n;
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
            nr++;
            for(j=i*2;j<=n;j=j+i) a[j]=1;
        }
    }

    out<<nr;
    in.close();
    out.close();

    return 0;
}