const int button = 12;
const int led = 4;

int lastButtonState = LOW;
int buttonState = LOW;

void setup() {
  Serial.begin(115200);
  pinMode(button, INPUT);
  pinMode(led, OUTPUT);
}

void loop() {
  buttonState = digitalRead(button);

  if (buttonState != lastButtonState) {
    if (buttonState == HIGH) {
      digitalWrite(led, !digitalRead(led));
    }
    delay(50);
  }

  lastButtonState = buttonState;
}