#include <bits/stdc++.h>
using namespace std;
const long long inf = (long long)1e15 + 88;
const int maxn = (int)1e6 + 88;
const int mod = 1000000007;
long long a[maxn];
long long b[maxn];
long long myabs(long long a) {
  if (a > 0)
    return a;
  else
    return -a;
}
int main() {
  long long n, m;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int i = 1; i <= m; i++) {
    cin >> b[i];
  }
  sort(b + 1, b + m + 1);
  b[0] = -inf;
  b[m + 1] = inf;
  long long dd;
  long long Max = 0;
  for (int i = 0; i < n; i++) {
    long long l = 0, r = m + 2;
    while (l <= r) {
      long long mid = (l + r) / 2;
      if (a[i] == b[mid]) {
        l = mid;
        break;
      } else if (b[mid] < a[i])
        l = mid + 1;
      else
        r = mid - 1;
    }
    dd = min(myabs(b[l] - a[i]), myabs(b[l - 1] - a[i]));
    Max = max(Max, dd);
  }
  cout << Max;
  return 0;
}
