#include <bits/stdc++.h>
using namespace std;
const int MAXN = 120000;
int n, m;
int a[MAXN];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> m;
  set<int> ss;
  int ans = 0;
  for (int i = 0; i < n; i++) cin >> a[i];
  for (int i = 1; i < m + 1; i++) {
    long long temp;
    cin >> temp;
    ss.insert(temp);
  }
  for (int i = 0; i < n; ++i) {
    int go = 2e9 + 100;
    auto it = ss.lower_bound(a[i]);
    if (it != ss.end()) go = min(go, *it - a[i]);
    if (it != ss.begin()) {
      --it;
      go = min(go, a[i] - *it);
    }
    ans = max(ans, go);
  }
  cout << ans;
}
