first = input()
x = first[0]
num = [0]
ans = []
n = 1
for i in range(1,len(first)):
    if x == first[i]:
        n += 1
    else:
        num.append(n)
        n=1
        x = first[i]
num.append(n)

for i in range(1,len(num)):
    ans.append(min(num[i-1],num[i]))
    
print(max(ans)*2)