#include <iostream>
#include <fstream>

std::ifstream fin("ciur.in");
std::ofstream fout("ciur.out");

int n;
bool v[2005000];
int main()
{
  fin>>n;
  int countt=n-1;
  for(int i=2;i<=n;i++)
  {
    if(v[i])continue;
    for(int j=i*i;j<=n;j+=i)
    {
      if(!v[j])
      {
        countt--;
   //     std::cout<<j<<" ";
      }
      v[j]=true;
    }
  }
  fout<<countt;
}