#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int N,M; cin >> N >> M;
    multiset<int> S;
    while(N--){
        int a; cin >> a;
        S.insert(a);
    }
    auto memo = S;
    vector<int> T;
    while(M--){
        int a; cin >> a;
        auto itr = S.lower_bound(a);
        if(itr == S.end()) break;
        T.push_back(a),S.erase(itr);
    }
    M = T.size();
    sort(T.begin(),T.end());
    int answer = 0;
    S = memo;
    for(auto t : T){
        while(true){
            int s = *S.begin(); S.erase(S.begin());
            if(s >= t){answer = max(answer,s-t); break;}
        }
    }
    cout << answer << endl;
}