“used as value” in function call

What’s the proper way of calling functions when evaluating their values in conditional statements?

package main
import "fmt"
func main(){
        if sumThis(1,2) > sumThis(3,4){
                fmt.Println("test")
        } else {
                fmt.Println("derp")
        }
}
func sumThis(a, b int){
        return a+b
}

this returns error:

./test4.go:4: sumThis(1, 2) used as value
./test4.go:4: sumThis(3, 4) used as value
./test4.go:11: too many arguments to return

How would you write this in Go?