#include <fstream>

using namespace std;

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

int n, cnt;
bool prim[2000010];

int main()
{
    in >> n;

    for (int i = 2; i <= n; i++)
    {
        if (prim[i] == 0)
        {
            for (long long j = 1LL * i * i; j <= n; j = j + i)
                prim[j] = 1;

            cnt++;
        }
    }

    out << cnt;


    return 0;
}