int i;
int time=100;

void setup() {
  for(i=1;i<=6;i++) {
  pinMode(i, OUTPUT);
 }
}

void loop(){
  for(i=1;i<=6;i+){
  digitalWrite(i, HIGH);
  delay(time);
  digitalWrite(i, LOW);
  delay(time);
}
for(i=5;i>=2;i--)
  digitalWrite(i, HIGH);
  delay(time);
  digitalWrite(i, LOW);
  delay(time);
}