[백준 1157] 단어 공부

import java.util.Scanner;

public class Main {
    
    public static int[] getAlphabetCount(String str){
        int[] count = new int[26];

        for(int i=0; i<str.length(); i++){
            char ch = str.charAt(i);
            count[ch - 'A']++;
        }
        return count;
    }
    
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String str = sc.next().toUpperCase();

        int[] count = getAlphabetCount(str);

        int maxCount = -1;
        char maxAlphabet = '?';
  
        for(int i=0; i<26; i++){
            if(count[i] > maxCount){
                maxCount = count[i];
                maxAlphabet = (char)('A' + i);
            }else if(count[i] == maxCount){
                maxAlphabet = '?';
            }
        }
        System.out.println(maxAlphabet);
    }
}