s = input()
ans = 0
def united(stri):
    for a in stri:
        if a != stri[0]:
            return False
    return True

while (not united(s)) and len(s) >= 2:
    k = len(s)
    if k == 2:
        if s[0] != s[1]:
            ans += 2
        break
    for i in range(0,k-2):
        if s[i] != s[i+1]:
            if i == k - 2:
                s = s[:i]
            elif i == 0:
                s = s[i+2:]
            else:
                s = s[:i] + s[i+2:]
            ans += 2
            break
print(ans)