#define PIN_OUTPUT  12
#define PIN_INPUT   2

void setup() {
  pinMode(PIN_OUTPUT, OUTPUT);
  pinMode(PIN_INPUT, INPUT);

  attachInterrupt(digitalPinToInterrupt(PIN_INPUT), blink, CHANGE);
}

void loop() {
  // put your main code here, to run repeatedly:
}

void blink(void)
{
  int status = digitalRead(PIN_OUTPUT);
  digitalWrite(PIN_OUTPUT,!status);
}