#define BTN_PIN 4  // Define the button pin

void setup() {
    pinMode(LED_BUILTIN, OUTPUT);
    pinMode(BTN_PIN, INPUT);
}

void loop() {
    if (digitalRead(BTN_PIN) == HIGH) { // Case 1: Pin 4 connected to 5V
        digitalWrite(LED_BUILTIN, HIGH); // Turn on the LED
    } else { // Case 2: Pin 4 connected to GND
        digitalWrite(LED_BUILTIN, LOW); // Turn off the LED
    }
}