unsigned long previousMillis = 0;
int intenzita = 1;
int k = 1;
void setup() {
Serial.begin(9600);
pinMode(9, OUTPUT);
}

void loop() {
  if(millis()- previousMillis > 20){
  if(intenzita==255 ||intenzita==0)
  k = -k;
  intenzita = intenzita + k;
  analogWrite(9,intenzita);
  previousMillis = millis();
  Serial.print("Juhuu");
}
Serial.print("Ahoj");
}