#include <bits/stdc++.h>
using namespace std;
int n, m;
int a[100011];
vector<int> b;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int j = 0; j < m; j++) {
    int x;
    cin >> x;
    b.push_back(x);
  }
  int res = 0;
  for (int i = 0; i < n; i++) {
    vector<int>::iterator it = lower_bound(b.begin(), b.end(), a[i]);
    int r = INT_MAX;
    if (it != b.end()) {
      r = abs(*it - a[i]);
    }
    if (it != b.begin()) {
      it--;
      r = min(r, abs(*it - a[i]));
    }
    res = max(res, r);
  }
  cout << res << endl;
}
