package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	reader := bufio.NewReader(os.Stdin)
	writer := bufio.NewWriter(os.Stdout)
	defer writer.Flush()

	var t int
	fmt.Fscan(reader, &t)

	for i := 0; i < t; i++ {
		var n int
		var s string
		fmt.Fscan(reader, &n, &s)

		count := 0
		var ans string
		for j := 0; j < n; j++ {
			if (s[j]-'0')%2 != 0 {
				ans += string(s[j])
				count++
				if count == 2 {
					break
				}
			}
		}

		if count == 2 {
			fmt.Fprintln(writer, ans)
		} else {
			fmt.Fprintln(writer, "-1")
		}
	}
}