#include <bits/stdc++.h>
using namespace std;
const long long M = 3e5 + 7, mod = 1e9 + 7;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  {
    long long n, m;
    cin >> n >> m;
    set<long long> s1, s2;
    for (long long i = 1; i <= n; i++) {
      long long x;
      cin >> x;
      s1.insert(x);
    }
    for (long long i = 1; i <= m; i++) {
      long long x;
      cin >> x;
      s2.insert(x);
    }
    s2.insert(9 * (1e18));
    long long ans = 0;
    for (auto u : s1) {
      auto it = s2.upper_bound(u);
      long long x = abs(*it - u), y = 9 * (1e18);
      if (it != s2.begin()) {
        it--;
        y = abs((*it) - u);
      }
      ans = max(ans, min(x, y));
    }
    cout << ans << "\n";
  }
  return 0;
}
