#include <bits/stdc++.h>
using namespace std;
long long mod = 1e9 + 7, mod1 = 1e9 + 9;
double eps = 1e-16;
const long long N = 100005;
long long a[N], b[N];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long n, m;
  cin >> n >> m;
  for (long long i = 0; i < (n); i++) cin >> a[i];
  for (long long i = 0; i < (m); i++) cin >> b[i];
  long long lo = 0, hi = 1e10;
  while (lo < hi) {
    long long mi = (lo + hi) / 2;
    long long j = 0;
    long long fl = 0;
    for (long long i = 0; i < (m); i++) {
      long long le = b[i] - mi, ri = b[i] + mi;
      while (j < n) {
        if (a[j] < le) {
          fl = 1;
          break;
        }
        if (a[j] > ri) break;
        j++;
      }
      if (fl) break;
    }
    if (fl || (j != n))
      lo = mi + 1;
    else
      hi = mi;
  }
  cout << lo;
  return 0;
}
