#include <fstream>

using namespace std;

bool v[2000005];

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

int main ()
{
    int n, p;
    fin >> n;
    p = 0;
    for (int i = 2; i <= n; i++)
    {
        if (v[i] == 0)
        {
            for (int j = 2*i; j <= n; j = j + i)
                v[j] = 1;
            p++;
        }
    }
    fout << p << '\n';
    fin.close();
    fout.close();
    return 0;
}