View Compilation Error

0_0_1170160_14892.cpp: In function `int main()':
0_0_1170160_14892.cpp:54: error: no match for 'operator=' in 'e = Q.std::priority_queue<_Tp, _Sequence, _Compare>::top [with _Tp = Node, _Sequence = std::vector<Node, std::allocator<Node> >, _Compare = std::greater<Node>]'
0_0_1170160_14892.cpp:7: note: candidates are: Node& Node::operator=(const Node&)