bufio_scanner = []


def main():
    n = int(fmt_scan())
    a = [int(fmt_scan()) for _ in range(n)]
    a.sort()

    ans = 1
    for i, _ in enumerate(a):
        if i == 0:
            continue
        if a[i] == a[i - 1] + 1:
            ans = 2
    print(ans)


def fmt_scan() -> str:
    sc = bufio_scanner
    if len(sc) == 0:
        for v in reversed(input().split()):
            sc.append(v)
    res = sc[-1]
    sc.pop()
    return res


main()