const int led1 = 11;
const int led2 = 12; 
const int led3 = 10;// LED connected to pin 12
void setup() {
 pinMode(led1, OUTPUT);
 pinMode(led2, OUTPUT);
 pinMode(led3, OUTPUT);// pin 12 is an output
}
void loop() {
 digitalWrite(led1, HIGH);
 digitalWrite(led2, LOW);
 digitalWrite(led3, LOW);
 delay(500);
 digitalWrite(led1, LOW);
 digitalWrite(led2, HIGH);
 digitalWrite(led3, LOW);
 delay(500);// wait 1 second
 digitalWrite(led1, LOW);
 digitalWrite(led2, LOW);
 digitalWrite(led3, HIGH);
 delay(500);
}