#include <bits/stdc++.h>
using namespace std;
clock_t T;
constexpr auto EPS = 1e-7;
const int mod = (int)1e9 + 7;
const double pi = acos(-1);
int dx[] = {0, 0, 1, -1, 1, 1, -1, -1};
int dy[] = {1, -1, 0, 0, 1, -1, 1, -1};
long long gcd(long long a, long long b) { return (a) ? gcd(b % a, a) : b; }
long long lcm(long long a, long long b) { return (a * b) / gcd(a, b); }
void COME_BACK() {
  std::ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
}
int n, m;
vector<long long> c, t;
bool valid(long long mid) {
  for (int i = 0; i < n; i++) {
    long long mr = c[i] + mid, ml = c[i] - mid;
    auto it = lower_bound(((t).begin()), ((t).end()), c[i]);
    auto it1 = lower_bound(((t).begin()), ((t).end()), ml);
    bool f = 0;
    if (it != t.end())
      if (*it <= mr) f = 1;
    if (it1 != t.end())
      if (*it1 <= mr) f = 1;
    if (!f) return 0;
  }
  return 1;
}
int main() {
  COME_BACK();
  cin >> n >> m;
  c.resize(n);
  t.resize(m);
  for (int i = 0; i < n; i++) cin >> c[i];
  for (int i = 0; i < m; i++) cin >> t[i];
  long long l = 0, r = 2e18, ans = LLONG_MAX;
  while (l <= r) {
    long long mid = (l + r) / 2;
    if (valid(mid))
      ans = mid, r = mid - 1;
    else
      l = mid + 1;
  }
  cout << ans << "\n";
}
