#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,bool>;
#define rep(i, n) for(int i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()

int main(){
    int n,m;
    cin >> n >> m;
    vector<P> ab(n+m+2);
    rep(i,n+m){
        cin >> ab[i].first;
        ab[i].second = (i<n);
    }
    ab[n+m] = make_pair(-100100100100100,true);
    ab[n+m+1] = make_pair(100100100100100,true);
    sort(all(ab));
    ll prev, ans = 0, ma = 0;
    rep(i,n+m+2){
        if(ab[i].second){
            if(ma){
                ma = max(ma, ab[i].first - ab[i-1].first);
                ans += ab[i].first - prev - ma;
                ma = 0;
            }
            prev = ab[i].first;
        }else{
            ma = max(ma, ab[i].first - ab[i-1].first);
        }
    }
    cout << ans << endl;
    return 0;
}