#include <iostream>
#include <string>
#include <cstring>
using namespace std;
int main() // 처음 짠 코드 -> 시간 초과
{
string s;
cin >> s;
// 대문자로 변환
for (int i = 0; i < s.length(); i++)
s[i] = toupper(s[i]);
int max_count = 0;
char max_alpha;
for (int i = 0; i < s.length(); i++)
{
int count = 1;
cout<<s[i];
for (int j = i + 1; j < s.length(); j++)
{
if (s[i] == s[j])
count++;
}
if (count > max_count)
{
max_alpha = s[i];
max_count = count;
}
else if (count == max_count)
max_alpha = '?';
}
cout << max_alpha << endl;
}
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