bufio_scanner = []


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

    ans = n
    d = [0, 0]
    for v in a:
        d.sort()
        for i, di in enumerate(d):
            if v <= di - 2:
                d[i] = v
                ans -= 1
                break
        else:
            d[0] = v
    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()