fn main() {
    input! {
        l: u64,
        r: u64,
    }
    let mut p = vec![];
    enumerate_prime(7416193, |v| {
        if v > 2 {
            p.push(v as u64);
        }
    });
    for (i, &a) in p.iter().enumerate().take_while(|p| p.1.pow(4) <= r) {
        for &b in p[i + 1..].iter().take_while(|b| a * a * b.pow(2) <= r) {
            let m = a * a * b;
            let mut c = (b + 1).max((l + m - 1) / m);
            while m * c <= r {
                if is_prime_miller(c) {
                    println!("{}", m * c);
                    return;
                }
                c += 1;
            }
        }
    }
    println!("-1");
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
// ---------- begin miller-rabin ----------
pub fn is_prime_miller(n: u64) -> bool {
    if n <= 1 {
        return false;
    } else if n <= 3 {
        return true;
    } else if n % 2 == 0 {
        return false;
    }
    let pow = |r: u64, mut m: u64| -> u64 {
        let mut t = 1u128;
        let mut s = (r % n) as u128;
        let n = n as u128;
        while m > 0 {
            if m & 1 == 1 {
                t = t * s % n;
            }
            s = s * s % n;
            m >>= 1;
        }
        t as u64
    };
    let mut d = n - 1;
    let mut s = 0;
    while d % 2 == 0 {
        d /= 2;
        s += 1;
    }
    const B: [u64; 7] = [2, 325, 9375, 28178, 450775, 9780504, 1795265022];
    for &b in B.iter() {
        let mut a = pow(b, d);
        if a <= 1 {
            continue;
        }
        let mut i = 0;
        while i < s && a != n - 1 {
            i += 1;
            a = (a as u128 * a as u128 % n as u128) as u64;
        }
        if i >= s {
            return false;
        }
    }
    true
}
// ---------- end miller-rabin ----------
// ---------- begin enumerate prime ----------
fn enumerate_prime<F>(n: usize, mut f: F)
where
    F: FnMut(usize),
{
    assert!(1 <= n && n <= 5 * 10usize.pow(8));
    let batch = (n as f64).sqrt().ceil() as usize;
    let mut is_prime = vec![true; batch + 1];
    for i in (2..).take_while(|p| p * p <= batch) {
        if is_prime[i] {
            let mut j = i * i;
            while let Some(p) = is_prime.get_mut(j) {
                *p = false;
                j += i;
            }
        }
    }
    let mut prime = vec![];
    for (i, p) in is_prime.iter().enumerate().skip(2) {
        if *p && i <= n {
            f(i);
            prime.push(i);
        }
    }
    let mut l = batch + 1;
    while l <= n {
        let r = std::cmp::min(l + batch, n + 1);
        is_prime.clear();
        is_prime.resize(r - l, true);
        for &p in prime.iter() {
            let mut j = (l + p - 1) / p * p - l;
            while let Some(is_prime) = is_prime.get_mut(j) {
                *is_prime = false;
                j += p;
            }
        }
        for (i, _) in is_prime.iter().enumerate().filter(|p| *p.1) {
            f(i + l);
        }
        l += batch;
    }
}
// ---------- end enumerate prime ----------