Luogu_CF_702_C.cpp

#include <bits/extc++.h>
using namespace std;
namespace pbds = __gnu_pbds;
using ui = unsigned int;
using uli = unsigned long long int;
using li = long long int;
int main(void) {
  ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  size_t n, m;
  cin >> n >> m;
  vector<li> a(n), b(m);
  for (li& i : a) cin >> i;
  for (li& i : b) cin >> i;
  sort(a.begin(), a.end()), sort(b.begin(), b.end());
  a.erase(unique(a.begin(), a.end()), a.end()),
      b.erase(unique(b.begin(), b.end()), b.end());
  li l = 0, r = 4e9;
  while (l < r) {
    li mid = (l + r) >> 1;
    bool flag = true;
    size_t pos = 0;
    for (li const& i : b) {
      if (a[pos] + mid < i) {
        flag = false;
        break;
      }
      while (pos < n && a[pos] - mid <= i) ++pos;
      if (pos >= n) break;
    }
    if (pos < n) flag = false;
    flag ? r = mid : l = mid + 1;
  }
  cout << l;
  return 0;
}