#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[100005];
  int b[100005];
  int n, m;
  cin >> n >> m;
  {
    for (int i = 0; i < n; i++) cin >> a[i];
    for (int i = 0; i < m; i++) cin >> b[i];
    int dis, r = 0;
    for (int i = 0; i < n; i++) {
      int tmp = lower_bound(b, b + m, a[i]) - b;
      if (tmp == 0)
        dis = b[0] - a[i];
      else if (tmp == m)
        dis = a[i] - b[m - 1];
      else
        dis = min(b[tmp] - a[i], a[i] - b[tmp - 1]);
      r = max(r, dis);
    }
    cout << r << endl;
  }
  return 0;
}
