unsigned long blnkTme;
int ledState = 1;

void setup() {

Serial.begin(9600);
Serial.println(blnkTme);
//digitalWrite(LED_BUILTIN, HIGH);
}

void loop() {

  Serial.println(millis()); 
if round((millis() / 1000) % 2 == 0) {
  digitalWrite(LED_BUILTIN, HIGH);
  }
  else {
  digitalWrite(LED_BUILTIN, LOW);
  }
}