void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
   for(int i=0;i<=500;i++){
    Serial.println(i);
   }
   for(int i=500;i>=0;i--){
    Serial.println(i);
   }
}