How to deduced the most nested iterator type?

I would like to write a type trait that, given a ContainerType, is capable to deduce the most nested IteratorType, meaning that given for example a std::vector<int> or a std::vector<std::vector<int>> or a std::vector<std::vector<std::vector<int>>> always the same IteratorType will be deduced, as if it is an std::vector<int>.