import java.util.*;
public class Main{
    public static void main(String [] args){
        Scanner sc= new Scanner(System.in);
        String s= sc.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    }
} import java.util.*; util.* java public class Main{
    public static void main(String [] args){
        Scanner sc= new Scanner(System.in);
        String s= sc.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    }
} Main public static void main(String [] args){
        Scanner sc= new Scanner(System.in);
        String s= sc.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    } main {
        Scanner sc= new Scanner(System.in);
        String s= sc.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    } Scanner sc= new Scanner(System.in); sc new Scanner(System.in) String s= sc.nextLine(); s sc.nextLine() sc.nextLine 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++;
            else count=0;
            
            if(count>max) max=count;
        } 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++;
            else count=0;
            
            if(count>max) max=count;
        } {
            char c= s.charAt(i);
            if(c=='A'||c=='C'||c=='G'||c=='T') count++;
            else count=0;
            
            if(count>max) max=count;
        } char c= s.charAt(i); c s.charAt(i) s.charAt s i if(c=='A'||c=='C'||c=='G'||c=='T') 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++ count count=0 count 0 if(count>max) max=count; count>max count max max=count max count 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.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    }
} public class Main{
    public static void main(String [] args){
        Scanner sc= new Scanner(System.in);
        String s= sc.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    }
} Main
import java.util.*;
public class Main{
    public static void main(String [] args){
        Scanner sc= new Scanner(System.in);
        String s= sc.nextLine();
        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++;
            else count=0;
            
            if(count>max) max=count;
        }
        System.out.println(max);
    }
}