int input_pin = 2;
volatile int value;

void setupTimer3() {
    noInterrupts();
    // Clear registers
    TCCR3A = 0;
    TCCR3B = 0;
    TCNT3 = 0;

    // 1 Hz (16000000 / ((15624+1)*1024))
    OCR3A = 15624;
    // CTC
    TCCR3B |= (1 << WGM32);
    // Prescaler 1024
    TCCR3B |= (1 << CS32) | (1 << CS30);
    // Output Compare Match A Interrupt Enable
    TIMSK3 |= (1 << OCIE3A);
    interrupts();
}

void setup() {
    pinMode(input_pin, INPUT);
    attachInterrupt(digitalPinToInterrupt(input_pin), state, CHANGE);
    DDRC = 0xFF;
    setupTimer3();
    Serial.begin(9600);
}

void loop() {
    PORTC = (1 << PC4) | (1 << PC5) | (1 << PC6) | (1 << PC7);
    delay(1000);
    PORTC = (0 << PC4) | (0 << PC5) | (0 << PC6) | (0 << PC7);
    delay(1000);
}

void state() {
    value = digitalRead(input_pin);
    Serial.print("Input reading: ");
    Serial.println(value);
}

ISR(TIMER3_COMPA_vect) {
    PORTC ^= (1 << PC0) | (1 << PC1) | (1 << PC2) | (1 << PC3);
}