#include <bits/stdc++.h>
using namespace std;
long long int k, a[200005], n, m, res = 0;
pair<long long int, long long int> p[200005];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> p[i].first;
    p[i].second = 1;
  }
  for (int i = n; i < n + m; i++) {
    cin >> p[i].first;
    p[i].second = 2;
  }
  sort(p, p + (n + m));
  k = -99999999999999LL;
  for (int i = 0; i < m + n; i++) {
    a[i] = 99999999999999LL;
    if (p[i].second == 2)
      k = p[i].first;
    else
      a[i] = min(a[i], p[i].first - k);
  }
  k = 99999999999999LL;
  for (int i = m + n - 1; i >= 0; i--) {
    if (p[i].second == 2)
      k = p[i].first;
    else
      a[i] = min(a[i], k - p[i].first);
  }
  for (int i = 0; i < n + m; i++)
    if (p[i].second == 1) res = max(res, a[i]);
  cout << res << endl;
  return 0;
}
