code: public Counter<K1> sumInnerCounter() {
      Counter<K1> summed = new ClassicCounter<K1>();
      for (K1 key : this.firstKeySet()) {
        summed.incrementCount(key, this.getCounter(key).totalCount());
      }
      return summed;
    }
docs: Returns the counters with keys as the first key and count as the
  total count of the inner counter for that key
  
  @return counter of type K1