const int button = 2;
const int led = 11;    
int btn = 0;   
int last = 0;   
int value = 0;     
int a;
void setup() {
  pinMode(button, INPUT); 
  pinMode(led, OUTPUT);    
  Serial.begin(9600);
}
void loop() {
  btn = digitalRead(button); 
  if (btn == LOW && last == HIGH) {
   if(value == 0){
      value=75;
   }
   else if(value==75){
    value=125;
   }
   else if(value==125){
    value=175;
   }
   else if(value==175){
    value=0;
   }
    analogWrite(led,value);
    Serial.println(value);
  }
  last = btn;
  delay(50); 
}