int red = 2;
int blue = 3;
int green = 4;

void setup() {
  pinMode(2, OUTPUT);
  pinMode(3,OUTPUT);
  pinMode(4,OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(red,HIGH);
  delay(2000);
  digitalWrite(red,LOW);
  digitalWrite(blue,HIGH);
  delay(2000);
  digitalWrite(blue,LOW);
  digitalWrite(green,HIGH);
  delay(2000);
  digitalWrite(green,LOW);
}