const int ledPin = 9;
const int buttonPin = 2;

int buttonState = 0;
int befor_State = 0;

void setup() {
  // put your setup code here, to run once:
    pinMode(buttonPin, INPUT);
    pinMode(ledPin, OUTPUT);
}

void loop() {

  buttonState = digitalRead(buttonPin);
  if(buttonState == LOW & buttonState == befor_State) 
    digitalWrite(ledPin, HIGH);
  else 
    digitalWrite(ledPin, LOW);

}