import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	} main {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) char[] S = sc.next().toCharArray(); S sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc int max = 0; max 0 int tmp = 0; tmp 0 for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		} int i=0; int i=0; i 0 i<S.length i S.length S S.length i++ i++ i {
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		} {
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		} if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			} S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T' S[i] == 'C' S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T' S[i] == 'A' S[i] S i 'A' S[i] == 'G' S[i] S i 'G' S[i] == 'C' S[i] S i 'C' S[i] == 'T' S[i] S i 'T' {
				tmp += 1;
			} tmp += 1 tmp 1 {
				tmp = 0;
			} tmp = 0 tmp 0 if (tmp > max){
				max = tmp;
			} tmp > max tmp max {
				max = tmp;
			} max = tmp max tmp 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);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	}
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();

		int max = 0;
		int tmp = 0;
		for (int i=0; i<S.length; i++){
			if (S[i] == 'A' || S[i] == 'G' || S[i] == 'C' || S[i] == 'T'){
				tmp += 1;
			}else {
				tmp = 0;
			}
			if (tmp > max){
				max = tmp;
			}
		}
		System.out.println(max);
	}
}