import java.util.*;
public class Main {
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    
    int max = 0;
    for (int i = 0; i < S.length(); i++) {
      for (int j = i; j < S.length(); j++) {
        int length = getACGTLen(S, i, j);
        if (max < length) {
          max = length;
        }
      }
    }
    System.out.println(max);
  }
  
  private static int getACGTLen(String s, int from, int to) {
    int length = 0;
    for (int i = from; i <= to; i++) {
      if (ACGT(s.charAt(i))) {
        length++;
      } else {
        return 0;
      }
    }
    return length;
  }
  
  private static boolean ACGT(char c) {
    return c == 'A' || c == 'C' || c == 'G' || c == 'T';
  }
}
/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