#include <bits/stdc++.h>
int min(int a, int b) { return a < b ? a : b; }
int main() {
  static int aa[100000], bb[100000];
  int n, m, i, j, d, r;
  scanf("%d%d", &n, &m);
  for (i = 0; i < n; i++) scanf("%d", &aa[i]);
  for (i = 0; i < m; i++) scanf("%d", &bb[i]);
  r = 0;
  for (i = j = 0; i < n; i++) {
    while (j < m && aa[i] > bb[j]) j++;
    d = min(j > 0 ? aa[i] - bb[j - 1] : 2147483647,
            j < m ? bb[j] - aa[i] : 2147483647);
    if (r < d) r = d;
  }
  printf("%d\n", r);
  return 0;
}
