#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
bool prim[2000001];
int main()
{
    int n, cnt = 0;
    f >> n;
    for (int i = 2; i <= n; i++)
    {
        prim[i] = true;
    }
    for (int i = 2; i <= n; i++)
    {
        if (prim[i] == true)
        {
            cnt++;
            for (int j = i + i; j <= n; j += i)
                prim[j] = false;
        }
    }
    g << cnt;
    return 0;
}