Exercise: maximum of arguments

Write a function func maxOf(first int, rest ...int) int that returns the largest of its arguments.

• maxOf(3, 9, 4) → 9
• maxOf(7) → 7
• maxOf(-5, -2, -9) → -2

Constraints: there are from one to 1000 arguments, each from -1000000 to 1000000, and all of them may be negative; rest may be empty.

Do not add extra imports unless the task says so explicitly.