import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		String s = sc.next();

		int ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	}
} 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 ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		String s = sc.next();

		int ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	} main {

		Scanner sc = new Scanner(System.in);

		String s = sc.next();

		int ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc int ans = 0; ans 0 for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		} int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		} {
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		} int len = 0; len 0 for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			} int j=i; int j=i; j i j<s.length() j s.length() s.length s j++ j++ j {
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			} {
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			} char c = s.charAt(j); c s.charAt(j) s.charAt s j if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				} 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' {
					len++;
				} len++ len {
					break;
				} break; ans = Math.max(ans, len) ans Math.max(ans, len) Math.max Math ans len System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		String s = sc.next();

		int ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		String s = sc.next();

		int ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	}
} 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 ans = 0;
		for (int i=0; i<s.length(); i++){
			int len = 0;
			for (int j=i; j<s.length(); j++){
				char c = s.charAt(j);
				if (c == 'A' || c == 'C' || c == 'G' || c == 'T'){
					len++;
				} else {
					break;
				}
			}
			ans = Math.max(ans, len);
		}
		System.out.println(ans);
	}
}