#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
long long n, i, j;
long nr = 1;
int p[2000001];
int main ()
{
    f >> n;
    for (i = 3; i <= n; i += 2)
    {
        if (p[i] == 0)
        {
            nr ++;
            for (j = i + i + i; j <= n; j += i << 1)
            {
                p[j] = 1;
            }
        }
    }
    g << nr;
    return 0;
}