#include <bits/stdc++.h>
using namespace std;
long long cities[100100];
long long towers[100100];
int n, m;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> cities[i];
  }
  for (int i = 0; i < m; i++) {
    cin >> towers[i];
  }
  long long r = 0;
  int k = 0;
  for (int i = 0; i < n; i++) {
    long long curR = abs(cities[i] - towers[k]);
    while (k < m - 1 && abs(towers[k + 1] - cities[i]) <= curR) {
      curR = abs(towers[++k] - cities[i]);
    }
    r = max(r, curR);
  }
  cout << r;
}
