/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
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*******************************************************************************/

#include <fstream>
#include <math.h>

using namespace std;

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

int v[10000];
int
main ()
{
  int n, k = 0;
  cin >> n;
  for (int i = 2; i <= n; ++i)
    v[i] = 1;
  for (int i = 2; i <= n; ++i)
    {
      if (v[i] == 1)
	{
	  for (int j = i + i; j <= n; j += i)
	    v[j] = 0;
	  ++k;
	}

    }
  cout << k;

  return 0;
}