int prev = 0;

void setup() {
  Serial.begin(9600);

  pinMode(A0, INPUT_PULLUP);
}

void loop() {
  int press = !digitalRead(A0);

  if (press != prev) {
    if (press) {
      Serial.print("1");
    } else {
      Serial.print("0");
    }
  }

  prev = press;
}