#A
"""
a, b, c = map(int, input().split())
print(min(b//a, c))
"""
#B
"""
a, b, k = map(int, input().split())
for i in range(max(a, b), 0, -1):
    if a % i == 0 and b % i == 0:
        k -= 1
        if k == 0:
             print(i)
"""

#C
s = input()
an0 = 0
an1 = 0
for i in s:
    if s == "1":
        an1 += 1
    if s == "0":
        an0 += 1
print(min(an0, an1)*2)