#include <fstream>
#include <vector>
using namespace std;

ifstream fin;
ofstream fout;

vector <bool> prime (2000002 , 1);
int n, i, m, suma;


int main (void){
    fin.open("ciur.in");
    fin>>n;
    fin.close();

    for (i=2; i<=(n/2); i++)
        if (prime[i]){
            for (int j=i+i; j<=(n/2); j+=i)
                prime[j] = false;

            suma++;
        }

    fout.open("ciur.out");
    fout<<suma<<"\n";
    fout.close();

    return 0;
}