void setup() {
  // make pin 2 an input and turn on the
  // pullup resistor so it goes high unless
  // connected to ground:
  pinMode(2, INPUT_PULLUP);
  Keyboard.begin();
}

void loop() {
//if the button is pressed
  if(digitalRead(2)==LOW){
    //Send hexadecimal 'F1',
    Keyboard.write(0xC2);
  }
}