//package abc124.B;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		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();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		System.out.println(ans);
	}

} Main public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		System.out.println(ans);
	} main {
		
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		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 String t = "ACGT"; t "ACGT" int ans = 0 ans 0 cnt = 0; cnt 0 for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		} int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		} {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		} if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0; t.indexOf(s.charAt(i)) >= 0 t.indexOf(s.charAt(i)) t.indexOf t s.charAt(i) s.charAt s i 0 cnt++ cnt cnt = 0 cnt 0 ans = Math.max(ans, cnt) ans Math.max(ans, cnt) Math.max Math ans cnt 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();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		System.out.println(ans);
	}

} public class Main {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		System.out.println(ans);
	}

} Main
//package abc124.B;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = "ACGT";
		
		int ans = 0, cnt = 0;
		
		for (int i = 0; i < s.length(); i++) {
			if (t.indexOf(s.charAt(i)) >= 0) cnt++;
			else cnt = 0;
			ans = Math.max(ans, cnt);
		}
		
		System.out.println(ans);
	}

}
