
import java.util.Scanner;

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

		Scanner scan = new Scanner(System.in);
		String str = scan.next();
		
		char[] list = str.toCharArray();
		int count = 0;
		int ans = 0;
		for (char c : list) {
			if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
				count++;
				if (ans < count) {
					
					ans = count;
				}
			} else {
				count = 0;
			}
		}
		
		System.out.println(ans);
		
		scan.close();
	}
}
/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