import java.util.*;
public class Main {
	public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
      String s = sc.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.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.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      }
      System.out.println(max);
    }
} Main public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
      String s = sc.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      }
      System.out.println(max);
    } main {
       Scanner sc = new Scanner(System.in);
      String s = sc.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      }
      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 max = 0; max 0 for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      } int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      } {
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      } int count = 0; count 0 for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        } int j=i; int j=i; j i j<s.length() j s.length() s.length s j++ j++ j {
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        } {
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        } if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          } s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T' s.charAt(j)=='G' s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T' s.charAt(j)=='A' s.charAt(j) s.charAt s j 'A' s.charAt(j)=='C' s.charAt(j) s.charAt s j 'C' s.charAt(j)=='G' s.charAt(j) s.charAt s j 'G' s.charAt(j)=='T' s.charAt(j) s.charAt s j 'T' {
            count++;
          } count++ count {
            break;
          } break; max = Math.max(max,count) max Math.max(max,count) Math.max Math 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.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.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.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.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.next();
      int max = 0;
      //１文字目始まりから探す
      for(int i=0;i<s.length();i++){
        int count = 0;
        for(int j=i;j<s.length();j++){
          if(s.charAt(j)=='A' || s.charAt(j)=='C' || s.charAt(j)=='G' || s.charAt(j)=='T'){
            count++;
          }else{
            break;
          }
        }
        max = Math.max(max,count);
      }
      System.out.println(max);
    }
}