import java.util.*;

public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String[] sList = s.split("[^(ACGT)]", 0);

        if (sList.length != 0) {
            int[] iList = new int[sList.length];

            for (int i = 0; i < sList.length; i++) {
                iList[i] = sList[i].length();
            }
            Arrays.sort(iList);


            System.out.println(iList[iList.length - 1]);
        } else {
            System.out.println(0);
        }

    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz