#include <Servo.h>

const int buttonPin = 4;
const int servoPin = 13;

Servo myServo;

bool buttonPressed = false;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  myServo.attach(servoPin);
  myServo.write(0);
}

void loop() {
  if (digitalRead(buttonPin) == LOW && !buttonPressed) {
    myServo.write(90);
    buttonPressed = true;

    delay(500);
  }

  if (digitalRead(buttonPin) == HIGH && buttonPressed) {
    buttonPressed = false;
  }
}