void setup() {
  pinMode(20, INPUT);
  pinMode(9, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH);
}

void loop() {
  if(digitalRead(20)==HIGH){
    delay(20);
    digitalWrite(9,(!digitalRead(9)));
  }
  for(int i= 0;i<255;i++){
    analogWrite(13,i);
    delay(10);
  }
  delay(1000);
  for(int i= 255;i>0;i--){
    analogWrite(13,i);
    delay(10);
  }
  delay(1000);
}