Concatenate First and Last Name into One String

Given two strings, first_name and last_name, return a single string in the format "last, first".

Examples

concat_name("First", "Last") ➞ "Last, First"

concat_name("John", "Doe") ➞ "Doe, John"

concat_name("Mary", "Jane") ➞ "Jane, Mary"

Notes

• Don't forget to return the result.
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