const int led1 = 2;
const int led2= 3;

void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);

}

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

}