[백준] 1157 Node

const fs = require('fs');
const input = fs.readFileSync("/dev/stdin").toString().trim().toUpperCase();
const obj = {}

for(let i = 0; i < input.length; i++) {
    obj[input[i]] = obj[input[i]] ? obj[input[i]]+1 : 1
}

const MAX = Math.max(...Object.values(obj))
const KEY = [];
for(let key in obj) {
    if(obj[key] === MAX) {
        KEY.push(key)
    }
}

console.log(KEY.length > 1 ? '?' : KEY[0])