Three buttons on one analog pin

three_buttons_one_analog.ino

/*
       Arduino AD0
            |
  VCC---2K2---470---1k---
            |     |     |   
           Up   Down  Select  
          (SW1) (SW2) (SW3) 
            |     |     |    
  Gnd--------------------
*/

void setup() {
  Serial.begin(9600);
}

void loop() {
  int adc_key_in = analogRead(0);  // read the value from analog 0
  //value read: 0(SW1),180(SW2), 410(SW3), 1023(OPEN)
  
  Serial.println(adc_key_in);
  delay(1000);
}