最高分是多少

import java.util.Scanner;

public class Main {
    static int M;
    static int N;
    static int[] grades;

    public static void Update(int index, int grade){
        grades[index] = grade; 
    }

    public static int Query_Max(int start , int end){
        int max;
        if ( start > end){
            start += end;
            end = start - end;
            start -= end;
        }
        max = grades[start];
        for ( int i = start+1 ; i <= end ; i++){
            if ( max < grades[i]){
                max = grades[i];
            }
        }
        return max;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner in = new Scanner(System.in);
        while(in.hasNextInt()){
            M = in.nextInt();
            N = in.nextInt();
            grades = new int[M];
            for ( int i = 0 ; i < grades.length; i++){
                grades[i] = in.nextInt();
            }
            for ( int i = 0 ; i < N ; i++){
                String str = in.next();
                int A = in.nextInt();
                int B = in.nextInt();
                if ( "Q".equals(str)){
                    int max = Query_Max(A-1, B-1);
                    System.out.println(max);
                }else if ("U".equals(str)){
                    Update(A-1,B);
                }
            }
        }
        in.close();
    }

}