#include <fstream>

using namespace std;

const int VM=2000001;

bool c[VM];

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

int main()
{
    int n, a=0;
    in >> n;
    for (int i=2; i*i<=n; i++){
        if(!c[i]){
            for (int j=i*i; j<=n; j+=i){
                c[j]=true;
            }
        }
    }
    for (int i=2; i<=n; i++){
        if (!c[i] && i!=n){
            a++;
        }
    }
    out << a;
    return 0;
}