#include <fstream>
#include <bitset>

using namespace std;

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

const int VMAX = 1e6;
int n;
bitset <VMAX> c;

int main()
{
    in >> n;
    int cnt = 0;
    for (int i = 2; i * i <= n; i++)
    {
        if(!c[i])
        {
            for (int j = i * i; j <= n; j += i)
            {
                c[j] = 1;
            }
        }
    }
    for (int i = 2; i <= n; i++)
    {
        if(!c[i])
        {
            cnt++;
        }
    }
    out << cnt;
    return 0;
}