const int led1 = 3;
const int led2 = 9;
const int led3 = 17;
void setup(){
 pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(led3, OUTPUT);
}

void loop() {
 digitalWrite(led1, HIGH);
 digitalWrite(led2, LOW);
 digitalWrite(led3, LOW);
 delay(1000);
 digitalWrite(led1, LOW);
 digitalWrite(led2, HIGH);
 digitalWrite(led3, LOW);
 delay(1000);
 digitalWrite(led3, HIGH);
 digitalWrite(led1, LOW);
 digitalWrite(led2, LOW);
 delay(1000);
}