function main(input) {
    const args = input.split(/\n/);
    const N = parseInt(args[0], 10),
          cards = args[1].split(' ').map(n => parseInt(n, 10));

    var aSum = 0,
        bSum = 0;

    cards.sort().reverse().forEach((n, i) => {
        (i % 2 === 0)? aSum += n : bSum += n;
    });

    console.log(aSum - bSum);
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));
