function solve() {
    const addBtn = document.querySelector("body > form > button");
    let [bookInput, yearInput, priceInput] = Array.from(document.querySelectorAll("form > input"));
    const bookShelfOldBooks = document.querySelector("#outputs > section:nth-child(1) > div");
    const bookShelfNewBooks = document.querySelector("#outputs > section:nth-child(2) > div");
    let priceWrapper = document.querySelector("body > h1:nth-child(3)");
    let price = 0;

    addBtn.addEventListener('click', (e) => {
        e.preventDefault();
        checkForValidInputs();
    });

    function checkForValidInputs() {
        let year = Number(yearInput.value);
        let price = Number(priceInput.value);
        let type = '';
        if (bookInput.value !== '' && year > 0 && price > 0) {
            if (year >= 2000) {
                type = 'new';
            } else {
                type = 'old';
            }
            addNewBook(type, year, price);
        }
    }

    function addNewBook(type, y, p) {
        let divBook = document.createElement('div');
        divBook.classList.add('book');

        let par = document.createElement('p');
        par.textContent = `${bookInput.value} [${y}]`;

        let buyBtn = document.createElement('button');
        buyBtn.textContent = `Buy it only for ${p.toFixed(2)} BGN`;
        buyBtn.addEventListener('click', (e) => removeBookAndIcreaseProfit(p, e, type));


        divBook.appendChild(par);
        divBook.appendChild(buyBtn);

        if (type === 'new') {
            let newBooksBtn = document.createElement('button');
            newBooksBtn.textContent = `Move to old section`;
            newBooksBtn.addEventListener('click', () => moveToOldSection(divBook, newBooksBtn));

            divBook.appendChild(newBooksBtn);

            bookShelfNewBooks.appendChild(divBook);
        } else {
            p = p * 0.85;
            buyBtn.textContent = `Buy it only for ${p.toFixed(2)} BGN`;
            bookShelfOldBooks.appendChild(divBook);

        }

    }

    function removeBookAndIcreaseProfit(p, e, type) {
        price += p;
        priceWrapper.textContent = `Total Store Profit: ${+price.toFixed(2)} BGN`;
        let elementToRemove = e.target.parentElement;
        if (type === 'new') {
            bookShelfNewBooks.removeChild(elementToRemove);
        } else {
            bookShelfOldBooks.removeChild(elementToRemove);
        }


    }

    function moveToOldSection(child, btnToRemove) {
        bookShelfNewBooks.removeChild(child);
        child.removeChild(btnToRemove);
        bookShelfOldBooks.appendChild(child);

    }
}