#include <Servo.h>

const int BUTTON_PIN = 13;
const int FIRST_SERVO_PIN = 11;

Servo firstServo;

const float positionZero = 0.0;
const float positionRotated = 180.0;

boolean state = false;
boolean lastButtonState = HIGH;
boolean currentButtonState = HIGH;

void setup()
{
  pinMode(BUTTON_PIN, INPUT_PULLUP);

  firstServo.attach(FIRST_SERVO_PIN);
  firstServo.write(positionZero);
}

void loop()
{
  boolean currentButtonState = digitalRead(BUTTON_PIN);

  if (currentButtonState != lastButtonState &&
   currentButtonState == LOW) {
    if (state) {
      firstServo.write(positionZero);
      state = false;
    } else {
      firstServo.write(positionRotated);
      state = true;
    }
  }

  lastButtonState = currentButtonState;
  delay(50);
}