use std::io::{BufRead, Write};

const PMAX: usize = 5_000_000;

fn main () {
    let stdin = std::io::stdin();
    let stdout = std::io::stdout();
    let mut reader = std::io::BufReader::new(stdin.lock());
    let mut writer = std::io::BufWriter::new(stdout.lock());

    let mut prime_table = vec![true; PMAX + 1];
    prime_table[1] = false;
    for i in 2..=PMAX {
        if !prime_table[i] { continue; }
        let mut j = i + i;
        while j <= PMAX {
            prime_table[j] = false;
            j += i;
        }
    }

    let t: usize = {
        let mut buf = String::new();
        reader.read_line(&mut buf).unwrap();
        buf.trim_end().parse().unwrap()
    };

    for _ in 0..t {
        let (a, p): (usize, usize) = {
            let mut buf = String::new();
            reader.read_line(&mut buf).unwrap();
            let mut iter = buf.split_whitespace();
            (
                iter.next().unwrap().parse().unwrap(),
                iter.next().unwrap().parse().unwrap(),
            )
        };
    
        if prime_table[p] {
            writeln!(writer, "{}", a % p).unwrap();
        } else {
            writeln!(writer, "-1").unwrap();
        }
    }
}