题解 | #字母大小写转换#

import java.util.Scanner;
public class Main{
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        while(scan.hasNextLine()) {
            String str = scan.nextLine();
            if(str.matches("[a-z]")) {
                System.out.println(str.toUpperCase());
            } else {
                System.out.println(str.toLowerCase());
            }
        }
    }
}