64. Interrupt Operation

What will happen after executing the below code on Arduino UNO?

Note: Consider no noise is created from button press.

Code

#define LED_PIN 13      
#define SWITCH1 4  
#define SWITCH2 5  

void setup() {
    pinMode(LED_PIN, OUTPUT);        
    pinMode(SWITCH1, INPUT_PULLUP);
    pinMode(SWITCH2, INPUT_PULLUP);

    // Configure Timer1 in CTC (Clear Timer on Compare Match) mode
    TCCR1A = 0; // Ensure no settings in TCCR1A (Normal mode)
    TCCR1B = (1 << WGM12) | (1 << CS12) | (1 << CS10); // CTC mode, Prescaler = 1024
   
    OCR1A = 7812; // Set compare match value for approximately 500 ms delay 
   
    TIMSK1 |= (1 << OCIE1A); // Enable Timer1 compare match interrupt
   
    sei(); 
}

void loop() {
  if (digitalRead(SWITCH1) == LOW) cli();
  if (digitalRead(SWITCH2) == LOW) sei();
}

// Interrupt Service Routine (ISR) for Timer1 Compare Match A
ISR(TIMER1_COMPA_vect) {
    digitalWrite(LED_PIN, !digitalRead(LED_PIN));	 // Toggle the LED state on every timer interrupt
}