const int sensor = 13;
const int RLED = 12;
const int BLED = 11;

void setup() 
{
    pinMode(sensor, INPUT);
    pinMode(BLED, OUTPUT);
    pinMode(RLED, OUTPUT);
}

void loop() 
{
  int sensorInput = digitalRead(sensor);
  if(sensorInput == HIGH)
  {
    digitalWrite(RLED, HIGH);
    digitalWrite(BLED, LOW);
    delay(500);
    digitalWrite(RLED, LOW);
    digitalWrite(BLED, HIGH);
    delay(500);
  }
  else
  {
    digitalWrite(RLED, LOW);
    digitalWrite(BLED, LOW);
  }
}