function solve3 (input=[]) {
    let arr = input.shift().split('&');

    // let commands = input.shift().split(' | ');

    while ( input.length > 0      /*commands[0] !== 'Done'*/) {
        let commands = input.shift().split(' | ');
        let action = commands[0];
        let bookName = commands[1];
        let book2Name = commands[2];

        if (action === 'Add Book') {
            if (arr.includes(bookName)) {
                continue;
            } else {
                arr.unshift(bookName);
            }
        } else if (action === 'Take Book') {
            if (arr.includes(bookName)) {
                let index = arr.indexOf(bookName);
                arr.splice(index, 1);
            }
        } else if (action === 'Swap Books') {
            if (arr.includes(bookName) && arr.includes(book2Name)) {
                let index1 = arr.indexOf(bookName);
                let index2 = arr.indexOf(book2Name);
                let temp = arr[index1];
                arr[index1] = arr[index2];
                arr[index2] = temp;
            }
        } else if (action === 'Insert Book') {
            arr.push(bookName);
        } else if (action === 'Check Book') {
            let index = Number(bookName);
            if ( 0 < index && index < arr.length) {
                console.log(arr[index]);
            }
        }

        // commands = input.shift().split(' | ');
    }
    console.log(arr.join(', '));

}