const int red_led = 8;
const int green_led = 7;

void setup() {
  // put your setup code here, to run once:
pinMode(red_led, OUTPUT);
pinMode(green_led, OUTPUT);


}

void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(8, HIGH);
digitalWrite(7, LOW);
delay(200);

digitalWrite(8, LOW);
digitalWrite(7, HIGH);
delay(200);


}