use proconio::input;

fn main() {
    input! {
        t:usize,
        ab:[(usize,usize);t],
    }

    const INF: usize = std::usize::MAX;
    for (a, b) in ab {
        let c = b - a;
        if c == 0 {
            println!("0");
            continue;
        }
        let mut ans = INF;
        for d in divisors(c) {
            if c / d < a {
                continue;
            }

            ans = ans.min(c / d - a);
        }

        if ans != INF {
            println!("{}", ans);
        } else {
            println!("-1");
        }
    }
}

use math::*;
mod math {
    #[allow(dead_code)]
    pub fn pow(mut n: usize, mut e: usize, m: usize) -> usize {
        let mut res = 1;
        n %= m;
        while 0 < e {
            if e & 1 != 0 {
                res *= n;
                res %= m;
            }

            n *= n;
            n %= m;
            e >>= 1;
        }

        res
    }

    #[allow(dead_code)]
    pub fn gcd(a: usize, b: usize) -> usize {
        if b == 0 {
            a
        } else {
            gcd(b, a % b)
        }
    }

    #[allow(dead_code)]
    pub fn lcm(a: usize, b: usize) -> usize {
        a / gcd(a, b) * b
    }

    #[allow(dead_code)]
    pub fn prime_factor(mut n: usize) -> std::collections::HashMap<usize, usize> {
        let mut pfacs = std::collections::HashMap::new();
        for d in 2.. {
            if d * d > n {
                break;
            }

            while n % d == 0 {
                *pfacs.entry(d).or_insert(0) += 1;
                n /= d;
            }
        }
        if n != 1 {
            *pfacs.entry(n).or_insert(0) += 1;
        }

        pfacs
    }

    #[allow(dead_code)]
    pub fn divisors(n: usize) -> Vec<usize> {
        let mut divs = vec![];
        for d in (1..).take_while(|&d| d * d <= n) {
            if n % d == 0 {
                divs.push(d);
                if n / d != d {
                    divs.push(n / d);
                }
            }
        }

        divs
    }

    #[allow(dead_code)]
    pub fn eratosthenes_sieve(n: usize) -> Vec<usize> {
        let mut is_primes = vec![true; n + 1];
        is_primes[0] = false;
        is_primes[1] = false;
        let mut primes = vec![];

        for i in 2..=n {
            if !is_primes[i] {
                continue;
            }

            for j in (2 * i..=n).step_by(i) {
                is_primes[j] = false;
            }
        }

        for (val, is_prime) in is_primes.into_iter().enumerate() {
            if is_prime {
                primes.push(val);
            }
        }

        primes
    }

    #[allow(dead_code)]
    pub fn base_n(mut base10: usize, base: usize, len: usize) -> Vec<usize> {
        let mut base_n = vec![];
        for _ in 0..len {
            base_n.push(base10 % base);
            base10 /= base;
        }
        base_n.reverse();

        base_n
    }

    #[allow(dead_code)]
    pub fn div_floor(mut a: i64, mut b: i64) -> i64 {
        if b < 0 {
            a = -a;
            b = -b;
        }

        if a >= 0 {
            a / b
        } else {
            (a + 1) / b - 1
        }
    }

    #[allow(dead_code)]
    pub fn div_ceil(mut a: i64, mut b: i64) -> i64 {
        if b < 0 {
            a = -a;
            b = -b;
        }
        if a > 0 {
            (a - 1) / b + 1
        } else {
            a / b
        }
    }
}