void setup() 
{
  DDRF = 0xF0 ;
  DDRA = 0xFF ;
  DDRC = 0xFF ;
}

void loop() 
{
  PORTA = 0x01 ;
  unsigned char button = PINF ;
  if ((button & 0x01) == LOW)
  {
    PORTA = 0x03 ;
  }
  if ((button & 0x02) == LOW)
  {
    PORTA = 0x07 ;
  }
}