#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e5 + 5;
long long int C[MAX], T[MAX], A = 1e9;
int main() {
  int N, M, i, j;
  long long int dist = -1;
  cin >> N >> M;
  for (i = 0; i < N; i++) {
    cin >> C[i];
    C[i] += A;
  }
  for (i = 0; i < M; i++) {
    cin >> T[i];
    T[i] += A;
  }
  j = 0;
  for (i = 0; i < N; i++) {
    while (j < M - 1 && abs(T[j] - C[i]) >= abs(T[j + 1] - C[i])) j += 1;
    dist = max(dist, abs(T[j] - C[i]));
  }
  cout << dist << "\n";
  return 0;
}
