#include <fstream>
#include <cmath>

using namespace std;

const int MAXN = 2000003;

bool prim[MAXN];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");

    int n;
    in >> n;

    int sol = 0;
    for (int i = 2; i <= n; i++)
        if (!prim[i])
        {
            sol++;
            for (int j = i; j <= n/i; j++)
            {
                prim[i * j] = 1;
            }
        }

    out << sol << '\n';

    return 0;
}