const int counter=5;
const int button1 = 12;
const int button2 = 11;
int button1state;
int button2state;

void setup()
{
for(int i=0; i<counter; i++){
pinMode(i, OUTPUT);
}
pinMode (button1, INPUT_PULLUP);
pinMode (button2, INPUT_PULLUP);
}

void loop()
{
button1state = digitalRead(button1);
button2state = digitalRead(button2);

if(button1state==LOW){
for(int i=counter;button2state==HIGH; i--){
flash(i, 100);
 if (i==0){
  i=counter;
 }
button2state = digitalRead(button2);
}
}

if(button2state==LOW){
for(int i=0;button1state==HIGH; i++){
flash(i, 100);
 if (i==counter){
  i=0;
 }
button1state = digitalRead(button1);
}
}
}

void flash(int led, int duration)
{
digitalWrite(led, HIGH);
delay(duration);
digitalWrite(led, LOW);
delay(duration);
}