int led = 9;
int knopka = 2;
bool sostKnopki;

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

void loop() {
  // put your main code here, to run repeatedly:
  sostKnopki = digitalRead(knopka);
  if (sostKnopki == LOW) {
    digitalWrite(led, LOW);
  }
  else {
    digitalWrite(led,HIGH);
  }
}