#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int arr[n], c[m];
  for (int i = 0; i < n; i++) cin >> arr[i];
  for (int i = 0; i < m; i++) cin >> c[i];
  long long mx = 0;
  for (int i = 0; i < n; i++) {
    int lo = 0, hi = m - 1, mid;
    while (lo < hi) {
      mid = lo + (hi - lo + 1) / 2;
      if (c[mid] <= arr[i]) {
        lo = mid;
      } else {
        hi = mid - 1;
      }
    }
    long long mn = abs(arr[i] - c[lo]);
    lo = 0, hi = m - 1;
    while (lo < hi) {
      mid = lo + (hi - lo) / 2;
      if (c[mid] >= arr[i]) {
        hi = mid;
      } else {
        lo = mid + 1;
      }
    }
    mn = min(mn, (long long)abs(arr[i] - c[lo]));
    mx = max(mx, mn);
  }
  cout << mx;
  return 0;
}
