Go Routing question

go_routine.go

package main

// Below is a function `sum()` that takes a number, runs a loop to add, and returns the result.
// In the main function, we call `sum()` once with a small number (e.g. 1000) and once
// with a large number (e.g. 1000000000) and prints the result. After that, the main()
// prints the string "All Done!"

// Your job is to convert the main() so that we call sum() concurrently, but wait for all the invocations
// to sum() to complete before printing "All Done".

import (
	"fmt"
)

func sum(num int) int {
	var res int
	for i := 1; i <= num; i++ {
		res += 1
	}
	return res
}

func main() {
	fmt.Println(sum(1000000000))
	fmt.Println(sum(1000))
	fmt.Println("All Done!")
}