no match for ‘operator+=’ aka std::_Rb_tree_const_iterator std::map [duplicate]

This question already has an answer here:

• Error: “no match for operator+” , for list iterator 4 answers

I have a map called assets returned from a const function, I use a const_iterator to get a subset of the map like this:

std::map<int, Asset>::const_iterator start = assets.begin();
start += 5;
......

But I got error: error: no match for ‘operator+=’ (operand types are ‘std::map<int, Asset>::const_iterator {aka std::_Rb_tree_const_iterator<std::pair<const int, Asset> >}’ and ‘int’)