#include <fstream>
using namespace std;

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

bool v[2000001];

int main()
{
    int N, gigel=0, i, j;
    in >> N;

    for (i=2; i<=N; i++)
    {
        if (v[i]==0)
        {
            gigel++;
            for (j=i*2; j<=N; j+=i)
            {
                v[j]=1;
            }
        }
    }

    out << gigel;

    return 0;
}