int GreenLED = 10;
int YellowLED = 11;
int RedLED = 12;

void setup() {
  // put your setup code here, to run once:
  pinMode(GreenLED, OUTPUT);
  pinMode(YellowLED, OUTPUT);
  pinMode(RedLED, OUTPUT);

  digitalWrite(GreenLED, LOW);
  digitalWrite(YellowLED, LOW);
  digitalWrite(RedLED, LOW);
  delay(1000);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(GreenLED, HIGH);
  digitalWrite(YellowLED, LOW);
  digitalWrite(RedLED, LOW);
  delay(1000);

  digitalWrite(GreenLED, LOW);
  digitalWrite(YellowLED, HIGH);
  digitalWrite(RedLED, LOW);
  delay(1000);

  digitalWrite(GreenLED, LOW);
  digitalWrite(YellowLED, LOW);
  digitalWrite(RedLED, HIGH);
  delay(1000);

  digitalWrite(GreenLED, LOW);
  digitalWrite(YellowLED, HIGH);
  digitalWrite(RedLED, LOW);
  delay(1000);
}