int led1 = 10;
int led2 = 5;
int dt = 500;
void setup() {
  // put your setup code here, to run once:
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
}
void loop() {
  // put your main code here, to run repeatedly:
  for(int i=1; i<=4; i++){
    if(i==1){
      digitalWrite(led1, HIGH);
      digitalWrite(led2, LOW);
      delay(dt);
    }
    else if(i==2){
      digitalWrite(led1, LOW);
      digitalWrite(led2, HIGH);
      delay(dt);
    }
    else if (i==3){
      digitalWrite(led1, HIGH);
      digitalWrite(led2, HIGH);
      delay(dt);
    }
    else {
      digitalWrite(led1, LOW);
      digitalWrite(led2, LOW);
      delay(dt);
    }
  }
}