#include <fstream>
using namespace std;

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

int n, cnt;
bool P[2000002];

int main()
{
    is >> n;
    P[1] = 1;
    for (int i = 2; i <= n; ++i)
        if (P[i] == 0)
        {
            cnt++;
            for (int j = i+i; j <= n; j+=i)
                P[j] = 1;
        }
    os << cnt << '\n';
    is.close();
    os.close();
    return 0;
}