a = input()
count0 = 0
count1 = 0
a = int(a)
while(a > 0):
    if(a%2 ==0):
        count0 = count0 + 1
        a = a/10
    else:
        count1 = count1 + 1
        a = (a-1)/10

print(min(count0,count1)*2)
