message: Update count-integers-in-intervals.cpp
diff: @@ -11,7 +11,7 @@ public:
  }
  void add(int left, int right) {
  - auto it = bst_.upper_bound({left + 1});
  + auto it = bst_.upper_bound({left});
  if (it != begin(bst_) && (*prev(it))[1] + 1 >= left) {
  --it;
  left = (*it)[0];
  