grade_develop = list(map(int, input().split()))
coup = []
coup_count = 0


def most_grade(develop_list):
    max_count_grade = 0
    counts = 0
    for idx, item in enumerate(develop_list):
        if develop_list.count(item) > counts:
            counts = develop_list.count(item)
            max_count_grade = item
    if counts == 1:
        return 'zero'
    else:
        return max_count_grade


if len(grade_develop) > 1:
    while len(grade_develop) > 1:
        max_grade = most_grade(grade_develop)
        for idx, item in enumerate(grade_develop):
            if max_grade != 'zero':
                if max_grade != item:
                    coup_count += 1
                    coup.append((item, max_grade))
                    del grade_develop[idx]
                    del grade_develop[grade_develop.index(max_grade)]
            else:
                for idx1, item1 in enumerate(grade_develop):
                    if item1 != item:
                        coup_count += 1
                        coup.append((item, item1))
                        del grade_develop[idx]
                        del grade_develop[grade_develop.index(item1)]
else:
    print(0)

print(coup_count)
for i in coup:
    print('{}, {}'.format(i[0], i[1]))