25

with open('24.txt') as f:
    a = f.read()
    cnt = float('-inf')
    b = 0
    for i in range(1, len(a)-1):
        if a[i] != a[i-1] and a[i] != a[i+1]:
            b += 1
            if cnt < b:
                cnt = b
        else:
            b = 0
print(cnt)