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(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > 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);
        
        String s = sc.next();
        
        int count = 0;
        int max = 0;
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        }
        
        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(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        }
        
        System.out.println(max);
    } main {
        
        Scanner sc = new Scanner(System.in);
        
        String s = sc.next();
        
        int count = 0;
        int max = 0;
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        }
        
        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(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        } {
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        } char c = s.charAt(i); c s.charAt(i) s.charAt s i if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                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++;
                if(count > max){
                    max = count;
                }
            } count++ count if(count > max){
                    max = count;
                } count > max count max {
                    max = count;
                } max = count 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);
        
        String s = sc.next();
        
        int count = 0;
        int max = 0;
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > 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);
        
        String s = sc.next();
        
        int count = 0;
        int max = 0;
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > 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);
        
        String s = sc.next();
        
        int count = 0;
        int max = 0;
        for(int i = 0; i < s.length(); i++){
            char c = s.charAt(i);
            if(c == 'A' || c == 'C' || c == 'G' || c == 'T'){
                count++;
                if(count > max){
                    max = count;
                }
            }else{
                count = 0;
            }
        }
        
        System.out.println(max);
    }
}