#include <bits/stdc++.h>
using namespace std;
int a[100005], b[100005];
int main() {
  int n, m, i, j, r;
  cin >> n >> m;
  for (i = 0; i < n; i++) cin >> a[i];
  for (i = 0; i < m; i++) cin >> b[i];
  r = 0;
  j = 0;
  for (i = 0; i < n; i++) {
    while (j < m - 1 && abs(b[j] - a[i]) >= abs(b[j + 1] - a[i])) j++;
    r = max(r, abs(b[j] - a[i]));
  }
  cout << r << "\n";
}
