#include <bits/stdc++.h>
using namespace std;
vector<int> vst(1000001);
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> c(n);
  vector<int> t(m);
  for (long long i = 0; i < n; i++) {
    cin >> c[i];
  }
  for (long long i = 0; i < m; i++) {
    cin >> t[i];
  }
  int i = 0, j = 0, d = 0, d1 = 0, d2 = 0, l, h, mid;
  if (t[0] > c[0]) {
    d2 = abs(c[0] - t[0]);
    d = max(d, abs(c[0] - t[0]));
    while (c[i] <= t[0]) {
      i++;
    }
  }
  while (1) {
    if (j < (m - 1)) {
      l = t[j];
      h = t[j + 1];
      mid = (h + l) / 2;
      while (c[i] <= h && c[i] >= l && i != n) {
        if (c[i] == mid) {
          d1 = min(abs(l - c[i]), abs(h - c[i]));
          d = max(d, d1);
        } else if (c[i] > mid) {
          d = max(d, abs(h - c[i]));
        } else if (c[i] < mid) {
          d = max(d, abs(l - c[i]));
        }
        i++;
      }
      j++;
    } else {
      break;
    }
  }
  if (c[n - 1] > t[m - 1]) {
    d = max(d, abs(c[n - 1] - t[m - 1]));
  }
  cout << d;
}
