def reverseShuffleMerge(s):
    # Write your code here
    
    stashed_dic = Counter(s)
    # the intial requirments for each char
    required_dic = {c:math.ceil(v/2) for c,v in stashed_dic.items()}
    
    result = []
    
    for c in reversed(s):
        stashed_dic[c] -= 1
        if required_dic[c] <= 0:
            continue
        # deal with the pop    
        while result:
            last_c = result[-1]
            if (c < last_c ) and (stashed_dic[last_c] >= required_dic[last_c] + 1):
                result.pop()
                required_dic[last_c] += 1 
            else:
                break
        result.append(c)
        required_dic[c] -= 1
        
    return  "".join(result)