#include<fstream>
using namespace std;
long long v[2000000], n, e;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main(){
    fin >> n;
    for (int i = 0; i < n; i++){
        v[i] = i;
        }
    for (int i = 2; i < n/2; i++){
        e = 2;
        if (v[i]){
                while (i * e < n){
            v[i*e] = 0;

            e++;
            }
            }
        }
        e = 0;
   for (int i = 2; i < n; i++){
       if(v[i]) e++;

       }
fout << e;
}