const uint16_t LUT[] = {30, 60, 90, 120};//extend as required
const int8_t LUTLen = sizeof(LUT) / sizeof(LUT[0]);
const int keypadAI = A0;
int8_t button = -1;
int8_t previous = -1;

void setup() {
  Serial.begin(115200);
}

void loop() {
  button = checkscan();
  if (button != -1 && button != previous) {
    Serial.println(button);
    previous = button;
  }
}

int checkscan() {//returns pad number(0-n), or -1
  int retval = -1;  //we return this if nothing pressed
  int rawval = analogRead(keypadAI);
  for (int i = 0; i < LUTLen; i++) {
    if (rawval < LUT[i]) { //if true, we've got one
      retval = i;
      delay(50);  //purely artificial, to prevent excess scrolling of SM
      break;
    }
  } //end of scan, either have button number or -1
  //implement your own debounce logic, if it's required
  return retval;
}