#include <fstream>

using namespace std;

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

int main(){
    int n,*v,s=0,aux,a;
    f>>n;
    f.close();
    v = new int[n];
    for(int i = 2;i<n;++i)
        v[i] = 0;
    for(int i = 2;i<n;++i)
        if(v[i] == 0){
            ++s;
            aux = i;
            a = i;
            while(aux < n){
                v[aux] = 1;
                aux += a;
            }
        }
    g<<s;
    g.close();
    return 0;
}