#include <fstream>

using namespace std;

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

const int N = 2000000;
bool c[N+1];

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