s = input()
now_word = ''
change_index_list = []

for index, word in enumerate(s):
    if index == 0:
        now_word = word
    
    if word != now_word:
        change_index_list.append(index)
        now_word = word
        
change_index_list.append(len(s))
change_index_list.insert(0, 0)

max_len = 0
candidate_index = 0

for index, change_index in enumerate(change_index_list):
    if index == 0:
        continue
    
    elif index == len(change_index_list) - 1:
        break
    
    else:
        candidate_index = min([change_index - change_index_list[index-1], change_index_list[index+1] - change_index])
        
    if max_len < candidate_index:
        max_len = candidate_index
    
print(2*max_len)