What's the Missing Letter?

Given a string of letters in the English alphabet, return the letter that's missing from the string. The missing letter will make the string be in alphabetical order (from A to Z).

If there are no missing letters in the string, return "No Missing Letter".

Examples

missingLetter("abdefg") ➞ "c"

missingLetter("mnopqs") ➞ "r"

missingLetter("tuvxyz") ➞ "w"

missingLetter("ghijklmno") ➞ "No Missing Letter"

Notes

The given string will never have more than one missing letter.