s = input()
n = len(s)
count = 0

while True:
    if '10' in s:
        count += s.count('10') * 2
        s = s.replace('10','')
    elif '01' in s:
        count += s.count('01','') * 2
        s = s.replace('01','')
    else:
        break

print(count)
