int LED1 = 2;  
int LED2 = 4;  
int LED3 = 5;  
int LED4 = 18;

void setup() {
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(LED3, OUTPUT);
  pinMode(LED4, OUTPUT);

  digitalWrite(LED1, LOW); 
  digitalWrite(LED2, LOW); 
  digitalWrite(LED3, LOW); 
  digitalWrite(LED4, LOW); 
}

void loop() {
  
  digitalWrite(LED1, HIGH);
  digitalWrite(LED2, LOW);
  digitalWrite(LED3, HIGH);
  digitalWrite(LED4, LOW);
  delay(1000); 

  
  digitalWrite(LED1, LOW);
  digitalWrite(LED2, HIGH);
  digitalWrite(LED3, LOW);
  digitalWrite(LED4, HIGH);
  delay(1000); 


}