const byte
LED1 = 3,
LED2 = 7
;

boolean LEDstate = false;

void setup ()
{
  pinMode ( LED1, OUTPUT );
  pinMode ( LED2, OUTPUT );
}

void loop ()
{
  LEDstate = ( millis () / 500 ) % 5;
  digitalWrite ( LED1, LEDstate );
  digitalWrite ( LED2, !LEDstate );
}