#include <fstream>

using namespace std;

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

int n, k;
bool a[2000001];

int main()
{
    f>>n;

    for (int i = 2; i <= n; ++i)
        a[i] = 1;
    for (int i = 2; i <= n; ++i)
        if (a[i])
        {
            ++k;
            for (int j = 2 * i; j <= n; j += i)
                a[j] = 0;
        }

    g<<k;   

    return 0;
}