int pinA = 3; 
void setup() {
  // put your setup code here, to run once:
pinMode(pinA, INPUT_PULLUP); 
}

void loop() {
  // put your main code here, to run repeatedly:
 if (digitalRead(pinA) == LOW)                     //Checking if the first switch has been pressed
  {
    Keyboard.write('A');                            //Sending the "A" character
    delay(500);
  }
}