#include <fstream>
#include <cmath>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
unsigned v[2000000], n, k, p;
int main()
{
    fin >> n;
    for (int i = 0; i <= n; i++)
    {
        v[i] = 1;
    }
    v[0] = 0;
    v[1] = 0;
    for (p = 2; p <= sqrt(n); p++)
    {
        if (v[p] == 1)
        {
            for (int j = 2; j * p <= n; j++)
            {
                v[p * j] = 0;
            }
        }
    }
    for (int i = 0; i <= n; i++)
        if (v[i] == 1) k++;
    fout << k;
    fout.flush();




    return 0;
}