#include <Arduino.h>
int X[16];
int Y[16];
int c = 0;
unsigned long lm = 0;
void setup() {
  DDRD |= 0b00111100;
  DDRB |= 0b00001111;
  PORTD &= ~0b00111100;
  PORTB |= 0b00001111;
  int i = 0;
  for (int y = 3; y >= 0; y--) {
    if ((3 - y) % 2 == 0) {
      for (int x = 0; x < 4; x++) {
        X[i] = x;
        Y[i] = y;
        i++;
      }
    } else {
      for (int x = 3; x >= 0; x--) {
        X[i] = x;
        Y[i] = y;
        i++;
      }
    }
  }
}
void loop() {
  if (millis() - lm >= 200) {
    lm = millis();

    PORTD &= ~0b00111100;
    PORTB |= 0b00001111;

    PORTD |= (1 << (Y[c] + 2));
    PORTB &= ~(1 << X[c]);

    c++;
    if (c >= 16) c = 0;
  }
}