#include <fstream>
using namespace std;
int v[2000001];
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n,i,j,nr=0;
    fin>>n;
    for (i=2;i*i<=n;i++) {
        if (v[i]==0) {
            for (j=i*i;j<=n;j=j+i) {
                v[j]=1;
            }
        }
    }
    for (i=2;i<=n;i++) {
        if (v[i]==0) {
            nr++;
        }
    }
    fout<<nr<<endl;
    fin.close();
    fout.close();
    return 0;
}