#define LedRed 25
#define LedYellow 26
void setup() {
  pinMode(LedRed, OUTPUT);
  pinMode(LedYellow, OUTPUT);
}

void loop() {
  digitalWrite(LedRed, HIGH);
  digitalWrite(LedYellow, LOW);
  delay(500);
  digitalWrite(LedRed, LOW);
  digitalWrite(LedYellow, HIGH);
  delay(500);
}