#define buttonPin A0
boolean buttonValue = 0;

#define ledPin 4

void setup(){
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(buttonPin), push, CHANGE);
}

void loop(){
  buttonValue = digitalRead(buttonPin);
  Serial.println(buttonValue);
  digitalWrite(ledPin, buttonValue);
  delay(100);
}

void push() {
  buttonValue = !buttonValue;
}