const int SWT1 = 3;        // the number of the pushbutton pin
const int LED1 = 2;

int start;
int lastMillis;

void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  pinMode(SWT1, INPUT_PULLUP);
  pinMode(LED1, OUTPUT);
  // digitalWrite(LED1, HIGH);
}

void loop() {

  if (!digitalRead(SWT1))
  {
    if (start == false)  // do we want to start the LED on/off cycle?
    {
      lastMillis = millis();      // initialize the timing
      digitalWrite(LED1, HIGH);  // turn LED on
      start = true;              // this prevents reinitializing lastMillis
    }
  }
    if ( millis() - lastMillis >= 20UL)  // if we in in checking mode, has the time expired?
    {
      digitalWrite(LED1, LOW);  // turn led off
      start = false;
       while(!digitalRead(SWT1)){}
       delay(10);              // For debouncing
    }
 
}