---

const byte BTN[3] = {3, 4, 5};
const byte LED[3] = {7, 8, 9};
byte state[3] = {0, 0, 0};

void setup() {
  for (byte i = 0; i < 3; i++) {
    pinMode(BTN[i], INPUT);
    pinMode(LED[i], OUTPUT);
  }
}

void loop() {
  byte sum = 0;
  for (byte i = 0; i < 3; i++) {
    if (digitalRead(BTN[i])) {
      state[i] ^= 1;
      delay(50);
    }
    sum += state[i];
  }
  for (byte i = 0; i < 3; i++)
    digitalWrite(LED[i], sum == i + 1);
}