int buttonState = 0; 
int buttonInput = PA3;
int LEDOutput = PA7;

void setup() {
  // initialize digital pin LEDOutput as an output.
  pinMode(LEDOutput, OUTPUT);
  
  // initialize digital pin buttonInput as an input.
  pinMode(buttonInput, INPUT);

 digitalWrite(LEDOutput, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(500);     
  digitalWrite(LEDOutput, LOW);   // turn the LED on (HIGH is the voltage level)
  delay(500);     
  
}

// the loop function runs over and over again forever
void loop() {

  //buttonState == HIGH, when do not press button
  //buttonState == LOW, when pressing button
  buttonState = digitalRead(buttonInput);

  //do not press button
  if (buttonState == HIGH) 
  {
    //turn LED off:
    digitalWrite(LEDOutput, LOW);
  } 
  //pressing button
  else 
  {
    //turn LED on:
    digitalWrite(LEDOutput, HIGH);
    delay(1000);                       // wait for a second
  }

}