#define led3 4
#define led2 5
#define led1 6 
 void setup()  {
 pinMode(led1, OUTPUT); // put your setup code here, to run once:
 pinMode(led2, OUTPUT);
 pinMode(led3, OUTPUT);
}

void loop() {
 digitalWrite(led1,HIGH);
 digitalWrite(led2, LOW);
 digitalWrite(led3,LOW); // put your main code here, to run repeatedly:
delay(3000);
digitalWrite(led1, LOW);
digitalWrite(led2, HIGH);
digitalWrite(led3, LOW);
delay(3000); 
digitalWrite(led1, LOW);
digitalWrite(led2, LOW);
digitalWrite(led3, HIGH);
delay(3000);
}