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)
}