#include <bits/stdc++.h>
using namespace std;
int a[100010];
int b[100010];
int ans[100010];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < (int)(n); ++i) cin >> a[i];
  for (int i = 0; i < (int)(m); ++i) cin >> b[i];
  int j = 0;
  for (int i = 0; i < (int)(n); ++i) {
    if (j < m - 1 && b[j + 1] < a[i]) {
      j++;
      i--;
      continue;
    }
    if (j < m - 1)
      ans[i] = min(abs(a[i] - b[j + 1]), abs(a[i] - b[j]));
    else
      ans[i] = abs(a[i] - b[j]);
  }
  cout << *max_element(ans, ans + n);
}
