#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define INF 1000000000
#define MOD 998244353
#define MAX 1000000

int main(){
  int N,M;
  cin>>N>>M;
  vector<pair<ll,int>> x;
  for(int i=0;i<N;i++){
    ll A;
    cin>>A;
    x.push_back(make_pair(A,1));
  }
  for(int j=0;j<M;j++){
    ll B;
    cin>>B;
    x.push_back(make_pair(B,0));
  }
  x.push_back(make_pair(-INF,1));
  x.push_back(make_pair(2*INF,1));
  sort(x.begin(),x.end());
  ll ans=x[N+M+1].first-x[0].first;
  ll y=0;
  for(int i=0;i<=N+M;i++){
    y=max<ll>(y,x[i+1].first-x[i].first);
    if(x[i+1].second==1){
      ans-=y;
      y=0;
    }
  }
  cout<<ans<<'\n';

}