import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        
        Scanner scanner = new Scanner(System.in);
        String S = scanner.next();
        int count = 0;
        int max = 0;
        
        for(int i=0; i<S.length(); i++){
            if(S.charAt(i)=='A'||S.charAt(i)=='G'||S.charAt(i)=='C'||S.charAt(i)=='T'){
                count++;
                if(max<=count){
                   max = count; 
                }
            }else{
                count = 0;
            }
        }
        
        System.out.println(max);
    }
}

/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