import numpy as np

np_int = np.frompyfunc(int,1,1)

s = np_int(np.array(list(input())))
del_num = 0

while True:
    old_s = s[:]
    del_list = np.full_like(s,False)
    for i in range(len(s) - 1):
        if (del_list[i] == True):
            continue
        if (str("".join(map(str,s[i:i + 2]))) == "01"):
            del_list[i:i + 2] = True
            for j in range(1,len(s)//2):
                if ("".join([str(s[i - j]), str(s[i + j + 1])]) == "01"):
                    del_list[i - j] = True
                    del_list[i + j + 1] = True
                else:
                    break
        if (str("".join(map(str,s[i:i + 2]))) == "10"):
            del_list[i:i + 2] = True
            for j in range(1,len(s)//2):
                if ("".join([str(s[i - j]), str(s[i + j + 1])]) == "10"):
                    del_list[i - j] = True
                    del_list[i + j + 1] = True
                else:
                    break
    s = np.delete(s, np.where(del_list == 1))
    del_num += np.sum(del_list)
    if (len(old_s) == len(s)):
        break

print(del_num)
