# -*- coding: utf-8 -*-

from collections import deque

def inpl(): return list(map(int, input().split()))



S = eval(input())

A = set("ATCG")

ans = 0

mode = 0

for i, s in enumerate(S):

    if s in A:

        if mode == 0:

            mode = 1

            start = i

    else:

        if mode == 1:

            ans = max(i - start, ans)

            mode = 0

if mode == 1:

    ans = max(len(S) - start, ans)

print(ans)
def inpl(): return list(map(int, input().split()))

S = eval(input())

C = set("ACGT")



tmp = 0

ans = 0



for s in S:

    if s in C:

        tmp += 1

    else:

        ans = max(ans, tmp)

        tmp = 0

ans = max(ans, tmp)

print(ans)
# -*- coding: utf-8 -*-
from collections import deque


def inpl():
    return list(map(int, input().split()))


S = eval(input())
A = set("ATCG")
ans = 0
mode = 0
for i, s in enumerate(S):
    if s in A:
        if mode == 0:
            mode = 1
            start = i
    else:
        if mode == 1:
            ans = max(i - start, ans)
            mode = 0
if mode == 1:
    ans = max(len(S) - start, ans)
print(ans)

def inpl():
    return list(map(int, input().split()))


S = eval(input())
C = set("ACGT")
tmp = 0
ans = 0
for s in S:
    if s in C:
        tmp += 1
    else:
        ans = max(ans, tmp)
        tmp = 0
ans = max(ans, tmp)
print(ans)

-# -*- coding: utf-8 -*- -from collections import deque - - -A = set("ATCG") +C = set("ACGT") +tmp = 0 -mode = 0 -for i, s in enumerate(S): -    if s in A: -        if mode == 0: -            mode = 1 -            start = i +for s in S: +    if s in C: +        tmp += 1 -        if mode == 1: -            ans = max(i - start, ans) -            mode = 0 -if mode == 1: -    ans = max(len(S) - start, ans) +        ans = max(ans, tmp) +        tmp = 0 +ans = max(ans, tmp)