#include <bits/stdc++.h>
using namespace std;
long long city[100007], tower[100007];
int n, m;
bool check(long long x) {
  int cp = 0;
  for (int i = 0; i < m; ++i) {
    while (abs(tower[i] - city[cp]) <= x) {
      ++cp;
      if (cp == n) return true;
    }
  }
  return false;
}
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; ++i) cin >> city[i];
  for (int i = 0; i < m; ++i) cin >> tower[i];
  long long low = 0, high = 1e10, ans = -1;
  while (low <= high) {
    long long x = low + (high - low) / 2;
    if (check(x))
      high = x - 1, ans = x;
    else
      low = x + 1;
  }
  cout << ans;
  return 0;
}
