const byte greenLedPin = 8;
const byte buttonPin = 7;

bool buttonState;
bool state = LOW;
bool greenLedState;
int counter = 0; 

void setup() {
  pinMode(greenLedPin, OUTPUT );
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
}

void loop() {

  buttonState = digitalRead(buttonPin);

  if (buttonState == HIGH) {
    counter++;
  } 

  else if (counter >= 5 && buttonState == LOW) {
      state = !state;
      counter = 0;
    }

  if (state == LOW) {
    digitalWrite(greenLedPin, HIGH);
  } else {
    digitalWrite(greenLedPin, LOW);
  }
}