const int ledRed = 6;
const int ledYellow = 3;
const int ledGreen = 4;

void setup() {
  pinMode(ledRed, OUTPUT);
  pinMode(ledYellow, OUTPUT);
  pinMode(ledGreen, OUTPUT);
}

void loop() {
  digitalWrite(ledRed,HIGH);
  delay(1000);
  digitalWrite(ledRed,LOW);
  delay(1000);
  digitalWrite(ledYellow,HIGH);
  delay(1000);
  digitalWrite(ledYellow,LOW);
  delay(1000);
  digitalWrite(ledGreen,HIGH);
  delay(1000);
  digitalWrite(ledGreen,LOW);
  delay(1000);
}