import java.util.Scanner;

public class Main {
  public static void main(String[] args) throws Exception {
    Scanner scanner = new Scanner(System.in);
    String a = scanner.next();
    int n = a.length();
    char[] b = a.toCharArray();
    scanner.close();

    int ans = 0;
    for (int i = 0; i < n; i++) {
      for (int j = i; j < n; j++) {
        int k = solve(b,i,j);
        if (ans < k) ans = k;
      }
    }
    System.out.println(ans);
  }

  private static int solve(char[] a, int i, int j) {
    for (int k = i; k <= j; k++) {
      if (a[k] == 'A' || a[k] == 'G' || a[k] == 'C' || a[k] == 'T') continue;
      return 0;
    }
    return j - i + 1;
  }
}
/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