const int LED = 9;
const int BUTTON = 5;
int BUTTON_PREVIOUS_STATE = HIGH;
int LED_LAST_STATE = LOW;
void setup(){
  pinMode(LED, OUTPUT);
  pinMode(BUTTON, INPUT_PULLUP);
}
void loop(){
  int BUTTON_CURRENT_STATE = digitalRead(BUTTON);
  if(BUTTON_CURRENT_STATE == LOW && BUTTON_PREVIOUS_STATE == HIGH){
    if(LED_LAST_STATE == LOW){
      digitalWrite(LED, HIGH);
      LED_LAST_STATE = HIGH;
    }
    else{
      digitalWrite(LED,LOW);
      LED_LAST_STATE = LOW;
    }
  }
  BUTTON_PREVIOUS_STATE = BUTTON_CURRENT_STATE;
}