import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    } main {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int count = 0; count 0 int max = 0; max 0 for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        } char c s.toCharArray() s.toCharArray s {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        } {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        } if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            } c == 'A' || c == 'C' || c == 'G' || c == 'T' c == 'G' c == 'A' || c == 'C' || c == 'G' || c == 'T' c == 'A' c 'A' c == 'C' c 'C' c == 'G' c 'G' c == 'T' c 'T' {
                count++;
            } count++ count {
                max = Math.max(max, count);
                count = 0;
            } max = Math.max(max, count) max Math.max(max, count) Math.max Math max count count = 0 count 0 max = Math.max(max, count) max Math.max(max, count) Math.max Math max count System.out.println(max) System.out.println System.out System System.out max String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int count = 0;
        int max = 0;
        for (char c : s.toCharArray()) {
            if (c == 'A' || c == 'C' || c == 'G' || c == 'T') {
                count++;
            } else {
                max = Math.max(max, count);
                count = 0;
            }
        }
      	max = Math.max(max, count);
        System.out.println(max);
    }
}
