function solve() {
    function makeEl(type, text, clazz) {
        let el = document.createElement(type);
        if (text !== null) {
            el.textContent = text;
        }
        if (clazz !== null) {
            el.setAttribute('class', clazz);
        }
        return el;
    }
    function makeBuyBtn(price, bookDiv) {
        let buyBtn = makeEl('button', `Buy it only for ${price} BGN`, null);
        buyBtn.addEventListener('click', function () {
            bookDiv.remove();
            profit += +price;
            document.getElementsByTagName('h1')[1].textContent = `Total Store Profit: ${profit} BGN`;
        });
        return buyBtn;
    }

    let btn = document.getElementsByTagName('button')[0];
    let oldBookShelf = document.getElementsByClassName('bookShelf')[0];
    let newBookShelf = document.getElementsByClassName('bookShelf')[1];
    let profit = 0;

    btn.addEventListener('click', function (e) {
        e.preventDefault();

        let [name, year, price] = Array.from(document.getElementsByTagName('input')).map(e => e.value);

        if (name === '' || year <= 0 || price <= 0) {
            console.log('Error');
            return;
        }
        let bookDiv = makeEl('div', null, 'book');
        bookDiv.appendChild(makeEl('p', `${name} [${year}]`, null));

        let priceNew = parseFloat(price).toFixed(2);
        let priceOld = (priceNew * 0.85).toFixed(2);

        if (+year < 2000) {
            bookDiv.appendChild(makeBuyBtn(priceOld, bookDiv));
            oldBookShelf.appendChild(bookDiv);

        } else {
            bookDiv.appendChild(makeBuyBtn(priceNew, bookDiv));

            let moveBtn = makeEl('button', `Move to old section`, null);
            moveBtn.addEventListener('click', function () {
                bookDiv.remove();
                bookDiv.lastChild.remove();
                bookDiv.lastChild.remove();
                bookDiv.appendChild(makeBuyBtn(priceOld, bookDiv));
                oldBookShelf.appendChild(bookDiv);
            });
            bookDiv.appendChild(moveBtn);
            newBookShelf.appendChild(bookDiv);
        }
    });
}