program ciurul_Eratostene;

  var n,k,i,c:longint;
      a:array [2..2000000] of byte;

      {a[i]=0 <=> i este numar prim
       a[i]=1 <=> i este numar compus}

begin
  assign(input,'ciur.in');
  reset(input);
  assign(output,'ciur.out');
  rewrite(output);

  readln(n);

  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;

  writeln(k);

  close(output);
end.