#include <bits/stdc++.h>
using namespace std;
const int maxn = 100005;
int a[maxn], b[maxn];
int n, m;
int main() {
  while (~scanf("%d%d", &n, &m)) {
    for (int i = 0; i < n; i++) scanf("%d", a + i);
    for (int i = 0; i < m; i++) scanf("%d", b + i);
    int dis, ans = 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]);
      ans = max(ans, dis);
    }
    printf("%d\n", ans);
  }
  return 0;
}
