/in/foo.cc: In function 'int main()':
/in/foo.cc:24:13: error: no matching function for call to 'std::priority_queue<long long int, std::vector<long long int>, std::greater<long long int> >::push()'
   heap.push();
             ^
In file included from /usr/include/c++/6/queue:64:0,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/stl_queue.h:558:7: note: candidate: void std::priority_queue<_Tp, _Sequence, _Compare>::push(const value_type&) [with _Tp = long long int; _Sequence = std::vector<long long int>; _Compare = std::greater<long long int>; std::priority_queue<_Tp, _Sequence, _Compare>::value_type = long long int]
       push(const value_type& __x)
       ^~~~
/usr/include/c++/6/bits/stl_queue.h:558:7: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/6/bits/stl_queue.h:566:7: note: candidate: void std::priority_queue<_Tp, _Sequence, _Compare>::push(std::priority_queue<_Tp, _Sequence, _Compare>::value_type&&) [with _Tp = long long int; _Sequence = std::vector<long long int>; _Compare = std::greater<long long int>; std::priority_queue<_Tp, _Sequence, _Compare>::value_type = long long int]
       push(value_type&& __x)
       ^~~~
/usr/include/c++/6/bits/stl_queue.h:566:7: note:   candidate expects 1 argument, 0 provided