#define A1 4
#define A2 2
#define B1 5
#define B2 18

void setup() {
  pinMode(A1, OUTPUT);  
  pinMode(A2, OUTPUT);  
  pinMode(B1, OUTPUT);  
  pinMode(B2, OUTPUT);  
     
}

void clear() {
  digitalWrite(A1, LOW);
  digitalWrite(A2, LOW);
  digitalWrite(B1, LOW);
  digitalWrite(B2, LOW);
}

void loop() {
  
  clear();
  digitalWrite(A1, HIGH);
  delay(100);

  clear();
  digitalWrite(B1, HIGH);
  delay(100);

  clear();
  digitalWrite(A2, HIGH);
  delay(100);

  clear();
  digitalWrite(B2, HIGH);
  delay(100);
  
}