How do I determine if a particular key is unique in a multimap?

I have a `multimap<key_type,value_type>` and I would like to know if a particular key appears in the map at most one time. I know I can call `multimap.equal_range(key)` to find an iterator to the start and end of the range containing `key` but I would like to know if there is only one element between the `range.first` and `range.second`. Is there a better way than incrementing the `range.first` value to see if it is equal to `range.end`? Since `multimap::iterator` is bidirectional it's not a huge deal to undo the increment but it seems sloppy to do that.