#include <bits/stdc++.h>
using namespace std;
int a[100000];
int b[100000];
int main() {
  int M, N;
  long long rm = 0, r, r1, r2, ns, ne, i, j, b0, bm, aa;
  cin >> N >> M;
  for (i = 0; i < N; i++) cin >> a[i];
  for (i = 0; i < M; i++) cin >> b[i];
  rm = 0;
  r = 0;
  if (a[0] < b[0]) rm = b[0] - a[0];
  if (a[N - 1] > b[M - 1]) r = a[N - 1] - b[M - 1];
  if (r > rm) rm = r;
  b0 = b[0];
  ns = 0;
  while (ns < N) {
    if (a[ns] <= b0)
      ns++;
    else
      break;
  }
  bm = b[M - 1];
  ne = N - 1;
  while (ne > 0) {
    if (a[ne] >= bm)
      ne--;
    else
      break;
  }
  j = 1;
  for (i = ns; i <= ne; i++) {
    aa = a[i];
    while (1) {
      if (aa <= b[j]) break;
      j++;
    }
    r1 = aa - b[j - 1];
    r2 = b[j] - aa;
    if (r1 > r2) r1 = r2;
    if (r1 > rm) rm = r1;
  }
  cout << rm;
  return 0;
}
