import java.io.PrintWriter
import java.util.*
import kotlin.math.*

fun PrintWriter.solve() {
    val numCases = nextInt()
    case@ for (_i in 0 until numCases) {
        val a = nextLong()
        val b = nextLong()
        // region divisors
        val number = b - a
        val divs = mutableListOf<Long>()
        var divisor = 1L
        while (divisor * divisor <= number) {
            if (number % divisor == 0L) {
                divs.add(divisor)
                if (divisor * divisor != number) {
                    divs.add(number / divisor)
                }
            }
            divisor++
        }
        // endregion
        var ans = Long.MAX_VALUE
        for (d in divs) {
            val x = (b - a) / d - a
            if (x >= 0 && (b + x) % (a + x) == 0L) {
                ans = minOf(ans, x)
            }
        }
        println(if (ans == Long.MAX_VALUE) -1 else ans)
    }
}

fun main() {
    Thread(null, {
        val writer = PrintWriter(System.out, false)
        writer.solve()
        writer.flush()
    }, "solve", abs(1L.shl(26)))
        .apply { setUncaughtExceptionHandler { _, e -> e.printStackTrace(); kotlin.system.exitProcess(1) } }
        .apply { start() }.join()
}

// region Scanner
private var st = StringTokenizer("")
private val br = System.`in`.bufferedReader()

fun next(): String {
    while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())
    return st.nextToken()
}

fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextLine() = br.readLine()
fun nextDouble() = next().toDouble()
// endregion