#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const long long INF = 2e18;
const int N = 1231234;
int n, m;
int a[N], b[N];
bool ok(long long x) {
  int i, j;
  for (i = 0, j = 0; i < m; ++i) {
    while (j < n && abs(b[i] - a[j]) <= x) j++;
  }
  return j == n;
}
int main() {
  while (cin >> n >> m) {
    int i, j;
    for (i = 0; i < n; ++i) scanf("%d", &a[i]);
    for (i = 0; i < m; ++i) scanf("%d", &b[i]);
    long long l = 0, r = INF;
    while (l <= r) {
      long long mid = (l + r) >> 1;
      if (ok(mid))
        r = mid - 1;
      else
        l = mid + 1;
    }
    printf("%I64d\n", l);
  }
}
