
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String s = scan.next();
        scan.close();

        int ans = 0;
        for (int i = 0; i < s.length(); i++) {
            for (int j = i+1; j <= s.length(); j++) {
                String a = s.substring(i, j);
                boolean isOK = true;
                for (int k = 0; k < a.length(); k++) {
                    char c = a.charAt(k);
                    if (c != 'A' && c != 'C' && c != 'G' && c != 'T') {
                        isOK = false;
                        break;
                    }
                }
                if (isOK) {
                    ans = Math.max(ans, a.length());
                }
            }
        }

        System.out.println(ans);
    }
}

/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