int i=1;

 

void setup() {


  pinMode(i,OUTPUT);


}

 

void loop() {

  

  for(i; i<6; i=i+1) {

    digitalWrite(i, HIGH);

    delay(20);

    digitalWrite(i, LOW);

  }

 

    for(i; i>1; i=i-1) {

    digitalWrite(i, HIGH);

    delay(20);

    digitalWrite(i, LOW);

  }

}