#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<long long> cities(n);
  set<long long> towers;
  for (auto &x : cities) cin >> x;
  for (int _ = (0); _ < int(m); ++_) {
    long long x;
    cin >> x;
    towers.insert(x);
  }
  towers.insert(-(1LL << 40));
  towers.insert(1LL << 40);
  long long ans = 0;
  for (auto &c : cities) {
    auto it = towers.lower_bound(c);
    long long cur = *it - c;
    --it;
    cur = min(cur, c - *it);
    ans = max(ans, cur);
  }
  cout << ans << endl;
}
