int ledPin = 13;
int x = 0;

unsigned long button_time = 0;
unsigned long last_button_time = 0;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledPin, OUTPUT);
  attachInterrupt(0, increment, RISING);
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(ledPin, LOW);
  delay(3000);
  Serial.println(x, DEC);
}

void increment() {
  button_time = millis();
  if (button_time - last_button_time > 250) {
    x++;
    digitalWrite(ledPin, HIGH);
    last_button_time = button_time;
  }
}