const int ledPin = LED_BUILTIN; //the number of the ledPin
//Variables will change 
int ledState = 0;   //set the ledstate to zero
unsigned long prev_millis = 0;
const long interval = 1000;//interval at which time to blink

void setup() {
  // put your setup code here, to run once:
pinMode(ledPin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
unsigned long current_millis =  millis();

if(current_millis - prev_millis >= interval ){
  prev_millis = current_millis;

  //if the LED is off turn it on and vice-versa:
 if(ledState == LOW){
  ledState = HIGH;
 } else{
  ledState =  LOW;
 }

//set the LED with the Ledstate of the variable:
digitalWrite(ledPin, ledState);


  }
}