const int LED_red=3;
const int LED_green=6;
void setup(){
  pinMode(LED_red,OUTPUT);
  pinMode(LED_green,OUTPUT);
}
void loop(){
  digitalWrite(LED_red,HIGH);
  digitalWrite(LED_green,LOW);
  delay(1000);
  digitalWrite(LED_red,LOW);
  digitalWrite(LED_green,HIGH);
  delay(1000);
}