import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
        String[] line = s.split("", 10);
        int count = 0;
        int max = 0;
        for(int i=0; i<line.length; i++){
          for(int j=0; j<line.length; j++){
        	if(line[j].equals("A") || line[j].equals("T") || line[j].equals("G") || line[j].equals("C")) {
              count++;
              if(count > max) {
           		 max = count;
              }
            }
            else count = 0;
          }
          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