int equalStacks(std::vector<int> h1, std::vector<int> h2, std::vector<int> h3) {
    std::multimap<int, std::vector<int>> stacks {  };
    stacks.insert({ std::accumulate(h1.begin(), h1.end(), 0), h1 });
    stacks.insert({ std::accumulate(h2.begin(), h2.end(), 0), h2 });
    stacks.insert({ std::accumulate(h3.begin(), h3.end(), 0), h3 });
    
    while (stacks.count(stacks.begin()->first) != stacks.size()) {
        auto max_sum { stacks.rbegin()->first };
        auto max_stacks { stacks.equal_range(max_sum) };
        auto max_stacks_copy { std::vector<decltype(stacks)::iterator>() };
        
        for (auto it = max_stacks.first; it != max_stacks.second; ++it) {
            max_stacks_copy.push_back(it);
        }
        
        for (auto it : max_stacks_copy) {    
            auto node { stacks.extract(it->first) };            
            node.key() -= *node.mapped().begin();
            node.mapped().erase(node.mapped().begin());
            
            stacks.insert(std::move(node));
        }
    }
    
    return stacks.begin()->first;
}