#include <fstream>
#include <bitset>
using namespace std;

int n;
bitset<2000001> c;

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

int ciur()
{
    int k = 0;
    for (int i = 2; i <= n; i++)
        if (!c[i])
        {
            k++;
            for (int j = i << 1; j <= n; j+=i)
                c[j] = 1;
        }
    return k;
}

int main()
{
    in >> n;
    out << ciur();
    return 0;
}