#include <fstream>

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