import numpy as np

s = list(input())
s = np.array(s)
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] == "T"):
            continue
        if (str("".join(s[i:i + 2])) == "01"):
            del_list[i:i + 2] = True
            for j in range(1,len(s)//2):
                if (0 <= i - j and i + j + 1 < len(s)) and ("".join([str(s[i - j]), str(s[i + j + 1])]) == "01"):
                    del_list[i - j] = True
                    del_list[i + j + 1] = True
                else:
                    break
        elif (str("".join(s[i:i + 2])) == "10"):
            del_list[i:i + 2] = True
            for j in range(1,len(s)//2):
                if (0 <= i - j and i + j + 1 < len(s)) and ("".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 == "T"))
    del_num += np.sum(len(np.where(del_list=="T")[0]))
    if (len(old_s) == len(s)):
        break
 
print(del_num)