#include<stdio.h>
int main() {
	char string[1000001] = { 0  };                           //문자열입력받음
	int cype[150] = { 0 };                                   //알파벳문자 대입용 
	int cpy = 0 , max = 1 , maxindex = 0,cnt = 0;            
 
	scanf("%s", string);
	for (int i = 0; string[i] != 0; i++) {
		if (string[i] >= 'a' && string[i] <= 'z')            //'a'~'z' 를 대문자로 변경
			string[i] -= 32;
		cpy = string[i];                                     
		cype[cpy]++;                                         //문자에 대응하는 값에 1씩추가
	}
 
	for (int j = 0; j < 150; j++) {
		if (max < cype[j]) {
			max = cype[j];
			maxindex = j;
			cnt = 0;                                         //최댓값이 변경되면 cnt값 0으로초기화
		}
		else if (max == cype[j])
			cnt++;                                           //반복횟수 문자가 중복-> cnt가 0보다 크게만들기
	}
	if (cnt > 0)                                             //반복횟수 문자가 여러개 -> ? 출력
		printf("?");
	else
		printf("%c", maxindex);                              //최대반복횟수 문자가 하나밖에없음
 
}

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YQ==

a