Reading from multiple channels simultaneously in Golang

I am new to Golang. Right now I am trying to figure out how to make an any-to-one channel in Golang, where the setup is as follows:

say I have two goroutines numgen1 and numgen2 executing concurrently and writing numbers to channels num1 resp. num2. I would like to add the numbers sent from numgen1 and numgen2 in a new process, addnum. I have tried something like this:

func addnum(num1, num2, sum chan int) {
    done := make(chan bool)
    go func() {
        n1 := <- num1
        done <- true
    }()
        n2 := <- num2
        <- done
    sum <- n1 + n2
}

but this seems sadly incorrect. Could someone please give me some ideas?

Thank you very much for your help.