N = input()  # 방 번호
 
 
def minimum_set(N):
    n = [int(i) for i in list(N)]
    n_count = []
    required_num = 0  # 필요한 세트
 
    for i in range(10):
        n_count.append(n.count(i))
 
    if n_count[6] == max(n_count) or n_count[9] == max(n_count):
        if (n_count[6] + n_count[9]) % 2 == 0:  # 6의 개수와 9의 개수가 짝수인 경우
            required_num = (n_count[6] + n_count[9]) / 2
        elif (n_count[6] + n_count[9]) % 2 != 0:  # 6의 개수와 9의 개수가 홀수인 경우
            required_num = ((n_count[6] + n_count[9]) / 2) + 1
    else:
        required_num = max(n_count)
 
    return int(required_num)
 
 
print(minimum_set(N))

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MTExNjY2

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