#include <fstream>

using namespace std;

const int N = 2000000;

bool c[N];

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

    int n;
    in >> n;
    for(int d = 2; d * d <= n; d++)
    {
        if(c[d] == false)
        {
            for(int m = d * d; m <= n; m += d)
            {
                c[m] = true;
            }
        }
    }
    int nr_prime = 0;
    for(int i = 2; i <= n; i++)
    {
        if(c[i] == false)
        {
            nr_prime++;
        }
    }
    out << nr_prime;

    in.close();
    out.close();
    return 0;
}