answer.code:21:9: error: ‘decltype(auto)’ type specifier only available with ‘-std=c++14’ or ‘-std=gnu++14’
   21 |         decltype(auto) operator()(Args &&...args) {
      |         ^~~~~~~~
answer.code:27:1: error: ‘decltype(auto)’ type specifier only available with ‘-std=c++14’ or ‘-std=gnu++14’
   27 | decltype(auto) y_combinator(Fun &&fun) {
      | ^~~~~~~~
answer.code: In function ‘int y_combinator(Fun&&)’:
answer.code:28:41: error: ‘decay_t’ is not a member of ‘std’; did you mean ‘decay’?
   28 |         return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
      |                                         ^~~~~~~
      |                                         decay
answer.code:28:41: error: ‘decay_t’ is not a member of ‘std’; did you mean ‘decay’?
   28 |         return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
      |                                         ^~~~~~~
      |                                         decay
answer.code:28:49: error: template argument 1 is invalid
   28 |         return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
      |                                                 ^~~
answer.code: At global scope:
answer.code:33:16: error: use of ‘auto’ in parameter declaration only available with ‘-std=c++14’ or ‘-std=gnu++14’
   33 | auto mul(const auto &first, const auto ...args) {
      |                ^~~~
answer.code:33:35: error: use of ‘auto’ in parameter declaration only available with ‘-std=c++14’ or ‘-std=gnu++14’
   33 | auto mul(const auto &first, const auto ...args) {
      |                                   ^~~~
answer.code:33:43: error: expansion pattern ‘const int’ contains no parameter packs
   33 | auto mul(const auto &first, const auto ...args) {
      |                                           ^~~~
answer.code:33:1: error: ‘mul’ function uses ‘auto’ type specifier without trailing return type
   33 | auto mul(const auto &first, const auto ...args) {
      | ^~~~
answer.code:33:1: note: deduced return type only available with ‘-std=c++14’ or ‘-std=gnu++14’
answer.code: In function ‘auto mul(...)’:
answer.code:34:31: error: ‘args’ was not declared in this scope
   34 |         return mul(first, mul(args...));
      |                               ^~~~
answer.code: In function ‘void solve()’:
answer.code:80:30: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’
   80 |                         auto [v, i] = que.top(); que.pop();
      |                              ^