int led1=23;
int led2=22;

void setup() {
  pinMode(23, OUTPUT);
  pinMode(22, OUTPUT);
  pinMode(21, OUTPUT);
}

void loop() {
  digitalWrite(23, 1);
  digitalWrite(22, 0);
  digitalWrite(21, 0);
  delay(500);
  digitalWrite(23, 0);
  digitalWrite(22, 1);
  digitalWrite(21, 0);
  delay(500);
  digitalWrite(23, 0);
  digitalWrite(22, 0);
  digitalWrite(21, 1);
  delay(500);
}