#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  int n, m;
  cin >> n >> m;
  vector<int> a(n), b(m);
  for (int i = 0; i < n; i++) cin >> a[i];
  for (int i = 0; i < m; i++) cin >> b[i];
  long long mx = -1e18 - 1;
  for (auto x : a) {
    auto it = upper_bound(b.begin(), b.end(), x);
    long long mn = 1e18 + 1;
    if (it != b.end()) mn = min(mn, 1ll * abs(x - *it));
    if (it != b.begin()) {
      it--;
      mn = min(mn, 1ll * abs(x - *it));
    }
    mx = max(mn, mx);
  }
  cout << mx;
}
