import sys
import numba


S_raw = sys.stdin.readline().strip()

@numba.jit
def check_next(S):
    S = list(S)
    before_num=S[0]
    for i in range(len(S)):
        if S[i]!=before_num:
            S.pop(i-1)
            #S = list(S)
            S.pop(i-1)
            new_S = S
            return S,1
            break
    return S,0


cnt=0
N=0

while cnt<50000:
    S_raw, check_cnt = check_next(S_raw)
    N += check_cnt
    if check_cnt==0:
        break
    cnt+=1
    
print(N*2)