#include <bits/stdc++.h>
using namespace std;
int n, m;
long long a[100100];
long long b[100100];
void read() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> a[i];
  for (int i = 0; i < m; i++) cin >> b[i];
}
bool check(long long r) {
  int p = 0;
  int q = 0;
  while (p < n) {
    if (b[q] - r <= a[p] && a[p] <= b[q] + r) {
      p++;
      continue;
    } else
      q++;
    if (q >= m) return false;
  }
  return true;
}
void solve() {
  long long a = 0;
  long long b = 2000000001;
  while (a < b) {
    int m = (a + b) / 2;
    if (check(m))
      b = m;
    else
      a = m + 1;
  }
  cout << a;
}
int main() {
  read();
  solve();
}
