#include <fstream>
#include <vector>

using std::vector;
std::ifstream in("ciur.in");
std::ofstream out("ciur.out");

vector <bool> a;

int main()
{
    int N;
    in >> N;

    a.resize(N,1);
    int cnt = 0;
    for (int i = 2; i <= N; i++)
        if (a[i] == 1)
    {
        cnt++;
        for (int j = i+i; j <= N; j += i)
            a[j] = 0;
    }

    out << cnt;
    return 0;
}