#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  long long a[n], b[m], c[n + m];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    c[i] = a[i];
  }
  for (int i = 0; i < m; i++) {
    cin >> b[i];
    c[n - 1 + i] = b[i];
  }
  long long r1 = 0, rmax = 0;
  long j = 0;
  for (int i = 0; i < n; i++) {
    while (a[i] > b[j] && j != m) {
      j++;
    }
    r1 = abs(a[i] - b[j]);
    if (r1 > abs(a[i] - b[j - 1]) && j != 0) r1 = abs(a[i] - b[j - 1]);
    rmax = max(rmax, r1);
  }
  cout << rmax;
  return 0;
}
