#include <fstream>
using namespace std;
bool v[2000100];
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int a;
    fin>>a;
    int s=0;
    for (int i=2;i<=a;++i)
    {
        if (v[i]==0)
        {
            for (int j=i;j<=a/i;++j)
            {
                v[j*i]=1;
            }
            s++;
        }
    }
    fout<<s;
}