#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> ara(n);
  for (int i = 0; i < n; i++) {
    cin >> ara[i];
  }
  set<int> lights;
  for (int i = 0; i < m; i++) {
    int x;
    cin >> x;
    lights.insert(x);
  }
  int ans = 0;
  for (int i = 0; i < n; i++) {
    int dist = INT_MAX;
    auto it = lights.lower_bound(ara[i]);
    if (it != lights.end()) {
      dist = (*it) - ara[i];
    }
    if (it != lights.begin()) {
      it--;
      dist = min(dist, (ara[i] - (*it)));
    }
    ans = max(ans, dist);
  }
  cout << ans << endl;
  return 0;
}
