#include <iostream>
#include <fstream>

using namespace std;

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

int n, nr = 1;
int OK[2000005];

int main()
{
    in >> n;

   for (int i = 2; i <= n; i++)
   {
       if (OK[i] == 0)
       {
           for (int j = i + i; j <= n; j = j + i)
            OK[j] = 1;

           nr++;
       }
   }

   out << nr;

   return 0;
}