#include <bits/stdc++.h>
using namespace std;
int N, M;
signed long long A[101010];
signed long long B[101010];
void solve() {
  int i, j, k, l, r, x, y;
  string s;
  cin >> N >> M;
  for (i = 0; i < (N); i++) cin >> A[i];
  B[0] = -1LL << 40;
  for (i = 0; i < (M); i++) cin >> B[i + 1];
  B[M + 1] = 1LL << 40;
  M += 2;
  signed long long mi = 0;
  for (i = 0; i < (N); i++) {
    x = lower_bound(B, B + M, A[i]) - B;
    mi = max(mi, min(A[i] - B[x - 1], B[x] - A[i]));
  }
  cout << mi << endl;
}
int main(int argc, char** argv) {
  string s;
  int i;
  if (argc == 1) ios::sync_with_stdio(false), cin.tie(0);
  for (i = 0; i < (argc - 1); i++) s += argv[i + 1], s += '\n';
  for (i = 0; i < (s.size()); i++) ungetc(s[s.size() - 1 - i], stdin);
  solve();
  return 0;
}
