// this constant won't change:
const int  buttonPin = 2;    // the pin that the pushbutton is attached to
const int ledPin = 13;       // the pin that the LED is attached to
// Variables will change:

int buttonPushCounter = 0;   // counter for the number of button presses
int buttonState = 0;         // current state of the button
int lastButtonState = 0;     // previous state of the button
void setup() {
  pinMode(buttonPin, INPUT); // initialize the button pin as a input
  pinMode(ledPin, OUTPUT); // initialize the LED as an output:
  Serial.begin(9600);
}

void loop() {
buttonState = digitalRead(buttonPin);  //讀取button狀態
// compare the buttonState to its previous state
  if (buttonState != lastButtonState) {
    // if the state has changed, increment the counter
    if (buttonState == HIGH) {
      // if the current state is HIGH then the button wend from off to on:
      buttonPushCounter++;
      Serial.println("on");
      Serial.print("number of button pushes:  ");
      Serial.println(buttonPushCounter);
    }
 else {  // if the current state is LOW then the button  wend from on to off:
      Serial.println("off");
    }
  //delay(50);   // Delay a little bit to avoid bouncing (波動), remove it if you want to see bouncing 
  }
  // save the current state as the last state,  for next time through the loop
  lastButtonState = buttonState;
  if (buttonPushCounter % 4 == 0) {
    digitalWrite(ledPin, HIGH);
  } else {
    digitalWrite(ledPin, LOW);
  }
}