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export default function countDaysTogether(    arriveAlice: string,    leaveAlice: string,    arriveBob: string,    leaveBob: string,): number {    const arrive = arriveAlice > arriveBob ? arriveAlice : arriveBob,        leave = leaveAlice < leaveBob ? leaveAlice : leaveBob,        base = (new Date(`2021-${leave}`).valueOf() -                    new Date(`2021-${arrive}`).valueOf()) /                (24 * 60 * 60 * 1000) + 1;    return Math.max(base, 0);}