use std::collections::BTreeMap;

use itertools::Itertools;
use proconio::input;

fn main() {
    input! {
        n: usize,
        m: usize,
        s: [usize; n],
        t: [usize; m],
    }

    let mut s_map = BTreeMap::new();
    for &s_i in &s {
        *s_map.entry(s_i).or_insert(0) += 1_usize;
    }
    let mut ss_map = s_map.clone();

    let mut end_j = m;
    for (j, &t_j) in t.iter().enumerate() {
        if let Some((&s_j, &cnt)) = s_map.range(t_j..).next() {
            if cnt == 1 {
                s_map.remove(&s_j);
            } else {
                s_map.insert(s_j, cnt - 1);
            }
        } else {
            end_j = j;
            break;
        }
    }

    let mut tt = t[..end_j].iter().collect_vec().clone();
    tt.sort();

    let mut ans: usize = 0;
    for &t_j in &tt {
        if let Some((&s_j, &cnt)) = ss_map.range(t_j..).next() {
            ans = ans.max(s_j - t_j);
            if cnt == 1 {
                ss_map.remove(&s_j);
            } else {
                ss_map.insert(s_j, cnt - 1);
            }
        }
    }

    println!("{}", ans);
}