void setup() {
  // put your setup code here, to run once:
  pinMode(8, INPUT_PULLUP);
  pinMode(9, INPUT_PULLUP);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  Serial.begin(115200);
}

int s1 = 0, s2 = 0;
unsigned long interval = 5000;
unsigned long start = millis();

void loop() {
  // put your main code here, to run repeatedly:
  if (digitalRead(8) == LOW && s2 == 0) { //代表S2按下
    s2 = 1;
    digitalWrite(2, HIGH);
    start = millis();
  }

  if (s2 == 1) {
    long int dif = millis() - start;
    // if (dif<0) dif+=
    Serial.println(dif);
    if (dif > interval) {
      digitalWrite(2, LOW);
      s2 = 0;
    }
  }

  if (digitalRead(9) == LOW && s1 == 0) { //P9 按下 且 s1 為0(表第一次按p9)
    if (digitalRead(3) == HIGH) {
      digitalWrite(3, LOW);
    } else {
      digitalWrite(3, HIGH);
    }
    s1 = 1; // p9 已按下過
  }

  if (digitalRead(9) == HIGH && s1 == 1) { // p9放開 且 s1==1 表p9被按下過
    s1 = 0; // p9 已放開
  }

}