var n,i,j,r:longint;
    v:array [1..2000000] of byte;
begin
 assign(input,'ciur.in');reset(input);
 assign(output,'ciur.out');rewrite(output);
 readln(n);
 for i:=2 to n do
  if v[i]=0 then begin
   for j:=2 to n div i do v[i*j]:=1;
   inc(r);
  end;
  writeln(r);
 close(input);close(output);
end.