#include <fstream>

using namespace std;

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

const int nmax= 2000000;

bool u[nmax+1];

int main() {
    int n, sol= 0;
    fin>>n;

    for ( int i= 2; i<=n; ++i ) {
        sol+= (1-u[i]);
        for ( int j= i*2; j<=n; j+= i ) {
            u[j]= 1;
        }
    }

    fout<<sol<<"\n";

    return 0;
}