int led0=13;
int led1=12;
int led2=11;
int led3=10;
int led4=9;
void setup() {
pinMode(led0, OUTPUT);
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(led3, OUTPUT);
pinMode(led4, OUTPUT);
}
void loop() {
for (int i=9; i<=13; i++){
  digitalWrite(i, HIGH);
  delay(100);
  digitalWrite(i, LOW);
}
for (int i=13; i>=9; i--){
  digitalWrite(i, HIGH);
  delay(100);
  digitalWrite(i, LOW);
}
}