int pinFrst = 12;
int pinScnd = 11;
int pinThr = 10;

int frstMode;
int scndMode;
int thrMode;

void setup() {
  Serial.begin(115200);
  Serial.println("Старт");
  pinMode(pinFrst, INPUT_PULLUP);
  pinMode(scndMode, INPUT_PULLUP);
  pinMode(thrMode, INPUT_PULLUP);
}

void loop() {
  int isPressedFrst = digitalRead(pinFrst);
  int isPressedScnd = digitalRead(pinScnd);
  int isPressedThr = digitalRead(pinThr);
  Serial.print("Кнопка 1: ");Serial.println(isPressedFrst);
  Serial.print("Кнопка 2: ");Serial.println(isPressedScnd);
  Serial.print("Кнопка 3: ");Serial.println(isPressedThr);
}