while(line = readline()) {
let length = 0, temp = '', reg = /[ATCG]/
for (let i = 0; i < line.length; i++) {
if (reg.test(line.charAt(i)) == true) {
temp += line.charAt(i)
length = temp.length > length ? temp.length : length
} else {
temp = ''
}
}
console.log(length)
}