#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
template <class T, class F>
T binarySearch(T ok, T ng, const F &f) {
	while (abs(ok - ng) > 1) {
		T mid = (ok + ng) / 2;
		(f(mid) ? ok : ng) = mid;
	}
	return ok;
}
int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n, m; cin >> n >> m;
	vector<int>s(n), t(m);
	rep(i, n)cin >> s[i];
	rep(i, m)cin >> t[i];
	auto f = [&](const long long x)->bool {
		multiset<int>mst;
		rep(i, n)mst.insert(s[i]);
		rep(i, x) {
			auto itr = mst.lower_bound(t[i]);
			if (itr == mst.end())return false;
			mst.erase(itr);
		}
		return true;
	};
	auto th = binarySearch<int>(0, m + 1, f);
	//	cout << th << endl;
	t.resize(th);
	sort(all(t));

	auto g = [&](const long long x)->bool {
		multiset<int>mst;
		rep(i, n)mst.insert(s[i]);
		for (auto e : t) {
			auto itr = mst.lower_bound(e);
			if (itr == mst.end())return false;
			if (*itr > e + x)return false;
			mst.erase(itr);
		}
		return true;
	};
	//cout << g(0) << endl;
	auto ans = binarySearch<int>(INF, -1, g);
	cout << ans << endl;
	return 0;
}
// 重いか？？