int num[256] = {0};
        vector<string>::iterator iter = text.begin();
        while (iter != text.end()){
            string st = *iter;
            for (int i = 0; i < st.size(); i++){
                int pos = st[i];
                num[pos]++;
            }
        }

        vector<int> index;

        int max = num[0];
        index.push_back(0);

        for (int i = 1; i < 256; i++){
            if (i == ' ') continue;
            if (num[i] > max){
                index.clear();
                max = num[i];
                index.push_back(i);
            }else if (num[i] == max){
                index.push_back(i);
            }
        }

        string res = "";
        int value;
        vector<int>::iterator iter2 = index.begin();
        while (iter2 != index.end()){
            value = *iter2;
            res += (char)value;
            iter2++;
        }

        return res;
        }