#include <bits/stdc++.h>
using namespace std;
int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  vector<long long int> a(n), b(m);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int i = 0; i < m; i++) {
    cin >> b[i];
  }
  sort(a.begin(), a.end());
  sort(b.begin(), b.end());
  long long int left = -1, right = 1e12;
  while (right - left > 1) {
    long long int mid = (left + right) / 2;
    bool ok = true;
    for (int i = 0; i < n; i++) {
      long long int l = a[i] - mid, r = a[i] + mid;
      auto it = lower_bound(b.begin(), b.end(), l);
      if (it == b.end()) {
        ok = false;
        break;
      }
      if (*it > r) {
        ok = false;
        break;
      }
    }
    if (ok) {
      right = mid;
    } else {
      left = mid;
    }
  }
  cout << right << endl;
}
