Closing in Sum

Create a function that returns the sum of the digits formed from the first and last digits, all the way to the center of the number.

Worked Example

closingInSum(2520) ➞ 72

// The first and last digits are 2 and 0.
// 2 and 0 form 20.
// The second digit is 5 and the second to last digit is 2.
// 5 and 2 form 52.

// 20 + 52 = 72

Examples

closingInSum(121) ➞ 13
// 11 + 2

closingInSum(1039) ➞ 22
// 19 + 3

closingInSum(22225555) ➞ 100
// 25 + 25 + 25 + 25

Notes

• If the number has an odd number of digits, simply add on the single-digit number in the center (see example #1).
• Any number which is zero-padded counts as a single digit (see example #2).