function solve(param) {
    let obj = {};
    let wordsList = param.split(' ').map(element => element.toLowerCase())

    for (let word of wordsList) {
        word = ' ' + word;
        if (!obj.hasOwnProperty(word)) {
            obj[word] = 1;
        } else {
            obj[word]++
        }
    }
    let result = [];
    let arr = Object.entries(obj)
    for (let [key, value] of arr) {
        if (value % 2 !== 0) {
            result.push(key)
        }

    }

    console.log(result.join(''))

}