void setup() 
     {  // initialize digital pin LED_BUILTIN as an output.           	
         pinMode(LED_BUILTIN, OUTPUT);
      }
void loop() {  
     digitalWrite(LED_BUILTIN, HIGH);  // turn the LED on
            delay(1000);   // wait for a second 
     digitalWrite(LED_BUILTIN, LOW);   // turn the LED off
            delay(1000);   // wait for a second
}