#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int N, rez;
char prim[2000005];
int main()
{ int i, j;
  in>>N;
  for(i=2;i<=N;++i)
    prim[i]=1;
  for(i=2;i<=N;++i)
    if(prim[i])
    { ++rez;
      for(j=i*2;j<=N;j+=i)
        prim[j]=0;
    }
  out<<rez;
  in.close();
  out.close();
  return 0;
}