#include <Servo.h>

Servo myservo;
int button_pin = 4;
int button_value;
void setup() {
  myservo.attach(9);
  pinMode(button_pin, INPUT_PULLUP);
}
void loop() {
  button_value = digitalRead(button_pin);

  if (button_value == 1) {
    myservo.write(0);
  } else if (button_value == 0) {
    myservo.write(180);
  }
  delay(50);
}