package main

import (
	"bufio"
	"bytes"
	"os"
)

type FastScanner struct {
	r *bufio.Reader
}

func (fs *FastScanner) NextInt64() int64 {
	var sign int64 = 1
	var val int64
	c, err := fs.r.ReadByte()
	for (c < '0' || c > '9') && c != '-' {
		c, err = fs.r.ReadByte()
		if err != nil {
			return 0
		}
	}
	if c == '-' {
		sign = -1
		c, _ = fs.r.ReadByte()
	}
	for c >= '0' && c <= '9' {
		val = val*10 + int64(c-'0')
		c, err = fs.r.ReadByte()
		if err != nil {
			break
		}
	}
	if err == nil {
		_ = fs.r.UnreadByte()
	}
	return val * sign
}

func main() {
	fs := &FastScanner{r: bufio.NewReaderSize(os.Stdin, 1<<20)}
	t := int(fs.NextInt64())
	var out bytes.Buffer
	for i := 0; i < t; i++ {
		x := fs.NextInt64()
		y := fs.NextInt64()
		if x == y {
			out.WriteString("-1\n")
			continue
		}
		m := x
		if y > m {
			m = y
		}
		p := int64(1)
		for p < m {
			p <<= 1
		}
		k := p - m
		out.WriteString(int64ToString(k))
		out.WriteByte('\n')
	}
	os.Stdout.Write(out.Bytes())
}

func int64ToString(x int64) string {
	if x == 0 {
		return "0"
	}
	var a [20]byte
	n := len(a)
	for x > 0 {
		n--
		a[n] = byte('0' + x%10)
		x /= 10
	}
	return string(a[n:])
}