int a;
int mode=0;
void setup() 
{
  for(a=0;a<9;a++)
    pinMode(a,OUTPUT);
  pinMode(13, INPUT);
}

void loop() 
{
  digitalWrite(0, HIGH);
  digitalWrite(13, LOW);
  if(13==HIGH)
  mode=1;
  for(a=1;a<9;a+=mode)
  {
    digitalWrite(a, HIGH);
    delay(500);
  }
  for(a=8;a>0;a-=mode)
  {
    digitalWrite(a, LOW);
    delay(500);
  }
}