#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<n;++i)
int main() {
    int n, m; cin >> n >> m;
    vector<int> a(n), b(m);
    rep(i,n)cin >> a[i];
    rep(i,m)cin >> b[i];
    vector<pair<int, bool>> x;
    for (int i = 0, j = 0; i < n || j < m;) {
        if (j == m || (i < n && a[i] < b[j])) {
            x.emplace_back(a[i++], true);
        }
        else {
            x.emplace_back(b[j++], false);
        }
    }

    int ans = x.back().first - x.front().first;
    int pre = -1, mac = 0;
    rep(i,n + m) {
        if (i) {
            mac = max(mac, x[i].first - x[i - 1].first);
        }
        if (x[i].second) {
            if (pre != -1)ans -= mac;
            pre = i, mac = 0;
        }
    }
    cout << ans << "\n";
    
    return 0;
}