void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(2, INPUT);
  pinMode(4, INPUT);
  pinMode(5, INPUT);
  pinMode(7, INPUT);
  pinMode(13, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  int i = 0;

  if(digitalRead(2) == HIGH)
  {
    i++;
  }
  if(digitalRead(4) == HIGH)
  {
    i++;
  }
  if(digitalRead(5) == HIGH)
  {
    i++;
  }
  if(digitalRead(7) == HIGH)
  {
    i++;
  }
  if(i>2)
  {
    digitalWrite(13, HIGH);
  }
  else
  {
    digitalWrite(13, LOW);
  }
}