void setup() {
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
}

void loop() {
  for(int i = 6; i <= 9; i++) {
    digitalWrite(i, HIGH); 
    if(i == 6)
      digitalWrite(9, LOW);
    else
      digitalWrite(i - 1, LOW);
    delay(200);
  }
}