a = list(map(int,list(input())))
c = 1
co = 0
p = a[0]
pp = []
for i in range(len(a)-1):
	if a[(i+1)] == p:
		c += 1
	else:
		pp.append(c)
		c = 1
		p = a[i+1]
ppp = pp[0]

kkk = 0
for i in range(len(pp)-1):
	if pp[i] >= 0:
		co += 2*(max(pp[i],pp[i+1]) - abs(pp[i] - pp[i+1]))
		pp[i+1] = pp[i+1] - pp[i]
	else:
		pp[i+1] = pp[i+1] - pp[i]
print(co)
