//#includ+++e <iostream>
#include <fstream>
using namespace std;


int main()
{

ifstream cin("ciur.in");
ofstream cout("ciur.out");
  long long int bun[100000], i, n, nr=0;
   cin >> n;
  for(i=2; i<=10000; i++)
    bun[i] = true;
  for(i = 2; i<=10000; i++)
  {
      if(bun[i]==true)
      {
          for(int j=2; j*i<=10000; j++)
            bun[i*j]= false;
      }
  }

  for( i=2; i<=n; i++)
    if(bun[i])
       nr++;
  cout << nr;
cin.close();
cout.close();
    return 0;
}