#include <bits/stdc++.h>
using namespace std;
long long n, m, md, c[100009];
long long a[100009], b[100009];
long long mx = -1e9 - 2;
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= m; i++) cin >> b[i];
  b[0] = b[1];
  b[m + 1] = b[m];
  for (int i = 1; i <= n; i++) {
    int l = 1;
    int r = m;
    while (l <= r) {
      md = (l + r) / 2;
      if (b[md] == a[i]) break;
      if (b[md] > a[i])
        r = md - 1;
      else if (b[md] < a[i])
        l = md + 1;
    }
    c[i] = min(abs(a[i] - b[md]), abs(a[i] - b[md - 1]));
    c[i] = min(c[i], abs(a[i] - b[md + 1]));
  }
  for (int i = 1; i <= n; i++) mx = max(c[i], mx);
  cout << mx;
}
