An integer interval `[a, b]` (for integers `a < b`) is a set of all consecutive integers from `a` to `b`, including `a` and `b`.

Find the minimum size of a set S such that for every integer interval A in `intervals`, the intersection of S with A has a size of at least two.

Example 1:

    Input: intervals = [[1,3],[1,4],[2,5],[3,5]]
    Output: 3
    Explanation: Consider the set S = {2, 3, 4}.  For each interval, there are at least 2 elements from S in the interval.
    Also, there isn't a smaller size set that fulfills the above condition.
    Thus, we output the size of this set, which is 3.

Example 2:

    Input: intervals = [[1,2],[2,3],[2,4],[4,5]]
    Output: 5
    Explanation: An example of a minimum sized set is {1, 2, 3, 4, 5}.

Constraints:

- `1 <= intervals.length <= 3000`
- `intervals[i].length == 2`
- `0 <= ai < bi <= 108`