const int buttonPin = 4;
const int ledPin = 12;
int buttonState;

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

}

void loop() {
  buttonState=digitalRead(buttonPin);
  if(buttonState==LOW){
    digitalWrite(ledPin, HIGH);
    delay(500);
    digitalWrite(ledPin, LOW);
    delay(500);
  }else{
    digitalWrite(ledPin,LOW);
  }
  // put your main code here, to run repeatedly:

}