#include <fstream>
#include <cmath>
using namespace std;
bool v[2000005];
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n,nr=0;
    fin>>n;
    int i,j;
    for (i=2;i<=n;i++) {
        v[i]=1;
    }
    for (i=2;i<=n;i++) {
        if (v[i]) {
            nr++;
            for (j=i+i;j<=n;j+=i) {
                v[j]=0;
            }
        }
    }
    fout<<nr;
fin.close();
fout.close();
return 0;
}