#include<iostream>
#include<fstream>
using namespace std;
int v[2000001],i,j,c,n;
int main()
{
  ifstream f("ciur.in");
  ofstream g("ciur.out");
  f>>n;
  for(i=2;i<=n/2;i++)
    if(!v[i])
  {
      c++;
      for(j=2*i;j<=n;j+=i)
        v[j]=1;
  }
  for(;i<=n;i++)
    if(!v[i])
     c++;
  g<<c;
  f.close();
  g.close();
  return 0;
}