#define LEDPIN   13
#define BUTTONPIN 2

bool buttonState = false;

void setup() {
  pinMode(LEDPIN,   OUTPUT);
  pinMode(BUTTONPIN, INPUT);
}

void loop() {
  buttonState = digitalRead(BUTTONPIN);
  if (buttonState) {
    digitalWrite(LEDPIN, HIGH);
    delay(50);
    digitalWrite(LEDPIN, LOW);
    delay(50);
  } else {
    digitalWrite(LEDPIN, LOW);
  }
}