# Equalize List Sums with Minimal Updates

You are given two lists of integers `a`

and `b`

where every element in both lists is between `1`

to `6`

. Consider an operation where you pick a number in either `a`

or `b`

and update its value to a number between `1`

to `6`

.

Return the minimum number of operations required such that the sum of `a`

and `b`

are equal. If it’s not possible, return `-1`

.

**Constraints**

`n ≤ 100,000`

where`n`

is the length of`a`

`m ≤ 100,000`

where`m`

is the length of`b`

https://binarysearch.com/problems/Equalize-List-Sums-with-Minimal-Updates

## Examples

### Example 1

**Input**

- a =
`[1, 5]`

- b =
`[6, 5, 5]`

**Output**

- answer =
`2`

**Explanation**

If we change the `1`

to `6`

in `a`

and the `6`

to `1`

in `b`

, then both of their sums would be `11`

.

### Example 2

**Input**

- a =
`[6]`

- b =
`[1, 1, 1, 1, 1, 1, 1]`

**Output**

- answer =
`-1`

**Explanation**

There’s no way to make `a`

and `b`

’s sums equal.

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