import java.util.*;
public class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String buf = " ";
		int N = S.length();
		int ans = 0;
		for(int i = 0;i < N;i++){
			for(int j = 0;j < i + 1;j++){
				buf = S.substring(j,N - i + j).replaceAll("[AGTC]","0");
				if(buf.matches("0*")){
					ans = S.substring(j,N - i + j).length();
					break;
				}
			}
			if(ans != 0){
				break;
			}
		}
		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