S = list(input())
S = [int(i) for i in S]
c = 0
#print(S)
while True:
    OK = 0
    flag = 0
    break_flag = 0
    for i in range(len(S)-1):
        if S[i] != S[i+1] and S[i] != 9 and S[i+1] != 9:
            S[i] = 9
            S[i+1] = 9
            OK += 1
        else:
            flag += 1
    #print(S)
    if flag == len(S)-1:
        break_flag = 1
    if OK >= 1:
        for i in range(2*OK):
            S.remove(9)
            c += 1
    #print(S)
    #print(flag)
    if break_flag == 1 or len(S) <= 1:
        break
print(c)