void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);
  pinMode(8, INPUT_PULLUP);

}

int cislo = 0;

void loop() {
  digitalWrite(13, HIGH);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);

  if (digitalRead(8) == LOW)
  {
    cislo++;
    Serial.println(cislo);

  }

}