int blueLedPin = 19;
int redLedPin = 18;
int yellowLedPin = 5;
int buttonPin = 15;

void setup() {
  pinMode(buttonPin, INPUT);
  pinMode(blueLedPin, OUTPUT);
  pinMode(redLedPin, OUTPUT);
  pinMode(yellowLedPin, OUTPUT);
}

void loop() {
  if(digitalRead(buttonPin) == HIGH) {
    digitalWrite(blueLedPin, HIGH);

    delay(500);
    digitalWrite(blueLedPin, LOW);
    digitalWrite(redLedPin, HIGH);

    delay(500);
    digitalWrite(redLedPin, LOW);
    digitalWrite(yellowLedPin, HIGH);

    delay(500);
    digitalWrite(yellowLedPin, LOW);
  } else {
    digitalWrite(blueLedPin, LOW);
    digitalWrite(redLedPin, LOW);
    digitalWrite(yellowLedPin, LOW);
  }
}