baekjoon 1157번

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main1157 {
    public static void main(String[] args) {
        int[] arr = new int[26];
        Scanner sc = new Scanner(System.in);
        String str = sc.next().toUpperCase();

        for(int i = 0; i < str.length(); i++){
            int idx = str.charAt(i);
            arr[idx - 'A']++;
        }

        int max = 0;
        char result = '?';

        for(int i = 0; i < arr.length; i++){
            if(max < arr[i]){
                max = arr[i];
                result = (char)(i + 65);
            }else if(max == arr[i]){
                result = '?';
            }
        }

        System.out.println(result);
    }
}