import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        //int N = sc.nextInt();
        char[] S = sc.next().toCharArray();
        int count=0;
        int max = 0;
        for(int i=0; i<S.length; i++){
            if(S[i]=='A' || S[i]=='G' || S[i]=='C' || S[i]=='T'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=0;
            }
        }

        
        
        
        
        
        
        
        
        
        
        
        
          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);
        //int N = sc.nextInt();
        char[] S = sc.next().toCharArray();
        int count=0;
        int max = 0;
        for(int i=0; i<S.length; i++){
            if(S[i]=='A' || S[i]=='G' || S[i]=='C' || S[i]=='T'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=0;
            }
        }

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

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

        
        
        
        
        
        
        
        
        
        
        
        
          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 count=0; count 0 int max = 0; max 0 for(int i=0; i<S.length; i++){
            if(S[i]=='A' || S[i]=='G' || S[i]=='C' || S[i]=='T'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=0;
            }
        } 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'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=0;
            }
        } {
            if(S[i]=='A' || S[i]=='G' || S[i]=='C' || S[i]=='T'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=0;
            }
        } if(S[i]=='A' || S[i]=='G' || S[i]=='C' || S[i]=='T'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=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' {
                  count++;
                  max = Math.max(max, count);
            } count++ count max = Math.max(max, count) max Math.max(max, count) Math.max Math max count {
                    count=0;
            } count=0 count 0 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);
        //int N = sc.nextInt();
        char[] S = sc.next().toCharArray();
        int count=0;
        int max = 0;
        for(int i=0; i<S.length; i++){
            if(S[i]=='A' || S[i]=='G' || S[i]=='C' || S[i]=='T'){
                  count++;
                  max = Math.max(max, count);
            }else{
                    count=0;
            }
        }

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

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

        
        
        
        
        
        
        
        
        
        
        
        
          System.out.println(max);
        }
    }