import java.io.IOException;
import java.util.Arrays;
import java.util.Scanner;
 
public class Main {
 
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String B = sc.nextLine();
    int max = 0; //the longest sequence of ACGT.
    int count = 0; //the longest current sequence of ACGT.
    for(int i=0; i<B.length(); i++) {
      if(B.charAt(i) == 'A' || B.charAt(i) == 'C' || B.charAt(i) == 'G' || B.charAt(i) == 'T') {
        count++;
      } else {
        
        max = Math.max(max, count);
        count = 0;
      }
    }
    max = Math.max(max, count);
    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