int switchState = 0;
void setup() {
pinMode(3, OUTPUT);
pinMode(2, INPUT);
}

void loop() {
  
  switchState = digitalRead(2) ;
if (switchState == LOW) // ako kopche != pritisnato
  {
    digitalWrite(3, HIGH);
    delay(500);
   digitalWrite(3, LOW);
    delay(500);
  }
else // ako kopche == pritisnato, ne trepka.
{
    digitalWrite(3, HIGH);
    
  
  }

 
}