void setup() {
  pinMode(19, OUTPUT); 
  pinMode(18, OUTPUT); 
  pinMode(21, OUTPUT); 
  pinMode(5, OUTPUT); 
}

void loop() {
  digitalWrite(19, HIGH); 
  digitalWrite(18, LOW);  
  digitalWrite(21, LOW);  
  digitalWrite(5, LOW);  
  delay(1000);

  digitalWrite(19, LOW);  
  digitalWrite(18, HIGH); 
  digitalWrite(21, LOW);   
  digitalWrite(5, LOW);   
  delay(1000);

  digitalWrite(19, LOW);  
  digitalWrite(18, LOW);  
  digitalWrite(21, HIGH); 
  digitalWrite(5, LOW);   
  delay(1000);

  digitalWrite(19, LOW);  
  digitalWrite(18, LOW);  
  digitalWrite(21, LOW);  
  digitalWrite(5, HIGH);  
  delay(1000);

  digitalWrite(19, HIGH); 
  digitalWrite(18, HIGH); 
  digitalWrite(21, LOW);   
  digitalWrite(5, LOW);    
  delay(1000);

  digitalWrite(19, LOW);   
  digitalWrite(18, LOW);   
  digitalWrite(21, HIGH);  
  digitalWrite(5, HIGH);   
  delay(1000);
}