void setup() {
  // put your setup code here, to run once:
for(int i=2;i<10;i++)
    pinMode(i, OUTPUT);

pinMode(A5, INPUT_PULLUP);

}
int on=0;
void loop() {
  // put your main code here, to run repeatedly:

if(digitalRead(A5)==0) 
{
  delay(5);
  on=(on+1)%2;
}
/*if(on==0) {digitalWrite(2, HIGH);digitalWrite(3, LOW);}else {digitalWrite(2, LOW);digitalWrite(3, HIGH);}*/
switch(on)
{
  case 0:
  for(int i=2;i<=9;i++)
  {
      digitalWrite(i, HIGH);  
      delay(250);
      digitalWrite(i, LOW);

      if(digitalRead(A5)==0) 
{
  delay(5);
  on=(on+1)%2;
}
  }
  for(int i=8;i>=3;i--)
  {
      digitalWrite(i, HIGH);  
      delay(250);
      digitalWrite(i, LOW);
      if(digitalRead(A5)==0) 
{
  delay(5);
  on=(on+1)%2;
}
  } 
  
  break;
  case 1:break;
  default:break;

}


}