#define BLUE 8U
#define PINK 9U
#define YELLOW 10U
#define ORANGE 11U
#define S1 12U
#define S2 13U

#define INTERVAL 1000u

void setup() {
  for(unsigned char i = 0; i < 5; i++)
    pinMode(BLUE + i, OUTPUT);
  pinMode(S1, INPUT);
  pinMode(S2, INPUT);
}

unsigned char c{};
bool both{};
long timestamp{};

void loop() {
  if (millis() >= timestamp && !digitalRead(S1)) {
    c = (c + both) % 4;
    digitalWrite(BLUE + c, true);
    if (!both)
      digitalWrite(BLUE + (!c ? 3 : (c - 1)), false);
    both = !both;
    timestamp = millis() + INTERVAL;
  }
}