import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final String S = sc.next();

        int max = 0;

        for (int i = 0; i < S.length(); i++) {
            int cnt = 0;
            for (int j = i; j < S.length(); j++) {
                final char cj = S.charAt(j);
                if (!isACGT(cj)) {
                    break;
                }
                cnt++;
            }
            max = Math.max(max, cnt);
        }

        System.out.println(max);
    }

    private static boolean isACGT(final char c) {
        return c == 'A' || c == 'C' || c == 'G' || c == 'T';
    }
}

/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