#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
struct Sync_stdio {
  Sync_stdio() {
    cin.tie(NULL);
    ios_base::sync_with_stdio(false);
  }
} _sync_stdio;
struct FAIL {
  FAIL() {
    cout << "CHANGE!!!"
         << "\n";
  }
};
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> a(n);
  vector<int> b(m);
  for (int __i = 0; __i < (n); ++__i) cin >> a[__i];
  ;
  for (int __i = 0; __i < (m); ++__i) cin >> b[__i];
  ;
  long long l = 0;
  long long r = 2000000001;
  while (l < r) {
    long long mid = (l + r) / 2;
    int j = 0;
    int res = 1;
    for (int i = (0); i < (n); ++i) {
      while (j < m && b[j] < a[i]) {
        ++j;
      }
      int flag = 0;
      if (j != 0 && abs(a[i] - b[j - 1]) <= mid) {
        flag = 1;
      }
      if (j != m && abs(a[i] - b[j]) <= mid) {
        flag = 1;
      }
      if (!flag) {
        res = 0;
        break;
      }
    }
    if (res) {
      r = mid;
    } else {
      l = mid + 1;
    }
  }
  cout << l;
}
