#define red 21
#define yellow 19
#define green 18
#define btn 5

int btnState = 0;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(red, OUTPUT);
  pinMode(yellow, OUTPUT);
  pinMode(green, OUTPUT);
  pinMode(btn, INPUT_PULLUP);

}

void loop() {
  byte btnState = digitalRead(btn);

  if (btnState==LOW){
    digitalWrite(red, HIGH);
    delay(50);
    digitalWrite(yellow, HIGH);
    delay(50);
    digitalWrite(green, HIGH);
    delay(50);
  }
  else{
    digitalWrite(red, LOW);
    delay(50);
    digitalWrite(yellow, LOW);
    delay(50);
    digitalWrite(green, LOW);
    delay(50);
  }
}