#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
long long n, m, a[N], b[N], ans, cnt = 1;
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];
  for (int i = 1; i <= n; i++) {
    while (cnt != m && abs(b[cnt] - a[i]) >= abs(b[cnt + 1] - a[i])) cnt++;
    if (abs(b[cnt] - a[i]) > ans) ans = abs(b[cnt] - a[i]);
  }
  cout << ans << endl;
}
