
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] c = sc.next().toCharArray();
		int cnt = 0;
		int ans = 0;

		sc.close();

		for (char d : c) {
			if (d != 'A' && d != 'C' && d != 'G' && d != 'T') {
				cnt = 0;
				continue;
			}
			cnt++;
			ans = Math.max(ans, cnt);
		}
		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