#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 7;
int n, m, ans;
int a[N], b[N];
inline int max(int x, int y) {
  if (x < y) return y;
  return x;
}
inline int min(int x, int y) {
  if (x > y) return y;
  return x;
}
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= m; i++) cin >> b[i];
  for (int i = 1; i <= n; i++) {
    int p = lower_bound(b + 1, b + 1 + m, a[i]) - b;
    if (p > m)
      ans = max(ans, abs(a[i] - b[p - 1]));
    else if (p <= 1)
      ans = max(ans, abs(b[1] - a[i]));
    else
      ans = max(ans, min(abs(a[i] - b[p]), abs(a[i] - b[p - 1])));
  }
  cout << ans;
  return 0;
}
