program ciurul_Eratostene;
  var f:text;
      n,k,i,c:longint;
      a:array [2..2000000] of byte;
begin
  assign(f,'ciur.in');
  reset(f);
  readln(f,n);
  close(f);
  for i:=2 to n do
    begin
      if a[i]=0 then
        begin
          inc(k);
          c:=2*i;
          while c<=n do begin a[c]:=1; c:=c+i; end;
        end;
    end;
  assign(f,'ciur.out');
  rewrite(f);
  writeln(f,k);
  close(f);
end.