const fn hash(mut n: usize) -> usize {
    while n >= 10 {
        let mut new_n = 0;
        while n > 0 {
            new_n += n % 10;
            n /= 10;
        }
        n = new_n;
    }
    n
}

fn get_primes(max: usize) -> Vec<usize> {
    let mut is_prime = vec![true; max + 1];
    is_prime[0] = false;
    is_prime[1] = false;

    for n in 2..=max {
        if !is_prime[n] {
            continue;
        }
        if n * n > max {
            break;
        }
        for i in ((n * n)..=max).step_by(n) {
            is_prime[i] = false;
        }
    }

    (0..=max).filter(|&n| is_prime[n]).collect()
}

fn main() {
    let mut xx = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut xx).ok();
    let xx: Vec<usize> = xx.split_whitespace().flat_map(str::parse).collect();

    let primes: Vec<usize> = get_primes(xx[1])
        .into_iter()
        .filter(|&n| n >= xx[0])
        .collect();
    let hashes: Vec<usize> = primes.iter().map(|&n| hash(n)).collect();

    let mut right = 0;
    let mut max_len = 0;
    let mut max_start = 0;

    for left in 0..hashes.len() {
        while right < hashes.len() && !&hashes[left..right].contains(&hashes[right]) {
            right += 1;
        }
        if right - left >= max_len {
            max_len = right - left;
            max_start = primes[left];
        }
    }

    println!("{max_start}");
}