You are given an array `tasks` where `tasks[i] = [actuali, minimumi]`:

- `actuali` is the actual amount of energy you spend to finish the `ith` task.
- `minimumi` is the minimum amount of energy you require to begin the `ith` task.

For example, if the task is `[10, 12]` and your current energy is `11`, you cannot start this task. However, if your current energy is `13`, you can complete this task, and your energy will be `3` after finishing it.

You can finish the tasks in any order you like.

Return the minimum initial amount of energy you will need to finish all the tasks.

Example 1:

    Input: tasks = [[1,2],[2,4],[4,8]]
    Output: 8
    Explanation:
    Starting with 8 energy, we finish the tasks in the following order:
        - 3rd task. Now energy = 8 - 4 = 4.
        - 2nd task. Now energy = 4 - 2 = 2.
        - 1st task. Now energy = 2 - 1 = 1.
    Notice that even though we have leftover energy, starting with 7 energy does not work because we cannot do the 3rd task.

Example 2:

    Input: tasks = [[1,3],[2,4],[10,11],[10,12],[8,9]]
    Output: 32
    Explanation:
    Starting with 32 energy, we finish the tasks in the following order:
        - 1st task. Now energy = 32 - 1 = 31.
        - 2nd task. Now energy = 31 - 2 = 29.
        - 3rd task. Now energy = 29 - 10 = 19.
        - 4th task. Now energy = 19 - 10 = 9.
        - 5th task. Now energy = 9 - 8 = 1.

Example 3:

    Input: tasks = [[1,7],[2,8],[3,9],[4,10],[5,11],[6,12]]
    Output: 27
    Explanation:
    Starting with 27 energy, we finish the tasks in the following order:
        - 5th task. Now energy = 27 - 5 = 22.
        - 2nd task. Now energy = 22 - 2 = 20.
        - 3rd task. Now energy = 20 - 3 = 17.
        - 1st task. Now energy = 17 - 1 = 16.
        - 4th task. Now energy = 16 - 4 = 12.
        - 6th task. Now energy = 12 - 6 = 6.

Constraints:

- `1 <= tasks.length <= 105`
- `1 <= actual​i <= minimumi <= 104`