int output = 0;

void setup()
{
  pinMode(0, OUTPUT);
  pinMode(1, OUTPUT);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(13, INPUT);
}

void loop()
{
// Why do bitwise ANDs throw an error???
  if (output == 0) {
    digitalWrite(0, LOW);
    digitalWrite(1, LOW);
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
  }
  if (output == 1) {
    digitalWrite(0, HIGH);
    digitalWrite(1, LOW);
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
  }
  if (output == 2) {
    digitalWrite(0, LOW);
    digitalWrite(1, HIGH);
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
  }
  if (output == 3) {
    digitalWrite(0, HIGH);
    digitalWrite(1, HIGH);
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
  }
  if (output == 4) {
    digitalWrite(0, LOW);
    digitalWrite(1, LOW);
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
  }
  if (output == 5) {
    digitalWrite(0, HIGH);
    digitalWrite(1, LOW);
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
  }
  if (output == 6) {
    digitalWrite(0, LOW);
    digitalWrite(1, HIGH);
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
  }
  if (output == 7) {
    digitalWrite(0, HIGH);
    digitalWrite(1, HIGH);
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
  }
  if (output == 8) {
    digitalWrite(0, LOW);
    digitalWrite(1, LOW);
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
  }
  if (output == 9) {
    digitalWrite(0, HIGH);
    digitalWrite(1, LOW);
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
  }
  if (output == 10) {
    digitalWrite(0, LOW);
    digitalWrite(1, HIGH);
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
  }
  if (output == 11) {
    digitalWrite(0, HIGH);
    digitalWrite(1, HIGH);
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
  }
  if (output == 12) {
    digitalWrite(0, LOW);
    digitalWrite(1, LOW);
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
  }
  if (output == 13) {
    digitalWrite(0, HIGH);
    digitalWrite(1, LOW);
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
  }
  if (output == 14) {
    digitalWrite(0, LOW);
    digitalWrite(1, HIGH);
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
  }
  if (output == 15) {
    digitalWrite(0, HIGH);
    digitalWrite(1, HIGH);
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
  }
  if (digitalRead(13) == LOW) {
    output = 0;
    delay(5);
  } else {
    delay(695);
    output++;
    if (output > 15) output = 0;
  }
}