#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll MOD = 1e9 + 7;
using vi = vector<int>;
using pi = pair<int, int>;
void setIO(string name = "") {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  if (name.size()) {
    freopen((name + ".in").c_str(), "r", stdin);
    freopen((name + ".out").c_str(), "w", stdout);
  }
}
int main() {
  setIO();
  ll n, m;
  cin >> n >> m;
  set<ll> xcords;
  set<ll> ccords;
  for (ll i = 0; i < n; ++i) {
    ll x;
    cin >> x;
    xcords.insert(x);
  }
  for (ll i = 0; i < m; ++i) {
    ll x;
    cin >> x;
    ccords.insert(x);
  }
  ll ans = 0;
  for (auto it = xcords.begin(); it != xcords.end(); ++it) {
    auto loc = ccords.lower_bound(*it);
    if (loc == ccords.begin()) {
      ans = max(ans, *loc - *it);
    } else if (loc == ccords.end()) {
      ans = max(ans, *it - *ccords.rbegin());
    } else {
      ans = max(ans, min(*loc - *it, *it - *(prev(loc, 1))));
    }
  }
  cout << ans << endl;
}
