int birta;

void setup() {
  Serial.begin(9600);
  pinMode(11, INPUT_PULLUP);
  pinMode(10, INPUT_PULLUP);
  pinMode(9, INPUT_PULLUP);   
  pinMode(5, OUTPUT); 
  analogWrite(5, 80*2.55);
  birta = 80;
  Serial.print(birta);
  Serial.println("%");
}

void loop() {
  if(digitalRead(11) == LOW) {    
    if(birta >= 10) {
      birta = birta - 10;
    }
    analogWrite(5, birta*2.55);
    Serial.print(birta);
    Serial.println("%");
    delay(250);
  }
  if(digitalRead(10) == LOW) {    
    if(birta <= 95) {
      birta = birta + 5;
    }
    analogWrite(5, birta*2.55);
    Serial.print(birta);
    Serial.println("%");
    delay(250);
  }
  if(digitalRead(9) == LOW) {    
    birta = 100;
    analogWrite(5, birta*2.55);
    Serial.print(birta);
    Serial.println("%");
    delay(250);
  }
}