int led = 13;
int outputLed = 2;
int interruptPin = 3;
volatile byte flag = LOW;
void pinChange ()
{
  flag = !flag;
  digitalWrite (outputLed, flag);
}

void setup ()
{
  pinMode (led, OUTPUT);
  pinMode(outputLed, OUTPUT);
  pinMode(interruptPin, INPUT_PULLUP);
  digitalWrite (outputLed, flag);
  attachInterrupt (digitalPinToInterrupt(interruptPin), pinChange, FALLING);
}

void loop ()
{
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}