#define buttonPin 3
#define LEDpin 2

void setup() {
  Serial.begin(9600);
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(LEDpin,OUTPUT);
 
  
  // put your setup code here, to run once:

}

void loop() {
  volatile bool buttonState = digitalRead(buttonPin);
  volatile bool buttonState_inv =! buttonState;
  digitalWrite(LEDpin, buttonState_inv);


  // put your main code here, to run repeatedly:

}