int mendel = 0;
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly

if (mendel<10){
  while (mendel<=10) {
   mendel = mendel+1;
   Serial.println(mendel);
   delay(500);
}
}
else (mendel>=0); {
  while (mendel>=0){
    mendel=mendel-1;
    Serial.println(mendel);
    delay(500);
  }

}
}