#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100100;
int n, m;
int a[MAXN], b[MAXN];
int main() {
  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 res = 0;
  res = max(res, b[0] - a[0]);
  res = max(res, a[n - 1] - b[m - 1]);
  int it = 0;
  for (int i = 0; i + 1 < m; ++i) {
    while (it < n && a[it] < b[i]) ++it;
    while (it < n && a[it] <= b[i + 1]) {
      res = max(res, min(a[it] - b[i], b[i + 1] - a[it]));
      ++it;
    }
  }
  printf("%d\n", res);
  return 0;
}
