#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;

int main(){

    int N, M, ans=0, mi;
    cin >> N >> M;
    vector<int> A(N), B(M);
    for (int i=0; i<N; i++) cin >> A[i];
    for (int i=0; i<M; i++) cin >> B[i];

    for (int i=0; i<N-1; i++){
        auto it1 = lower_bound(B.begin(), B.end(), A[i]);
        auto it2 = lower_bound(B.begin(), B.end(), A[i+1]);
        if (it2 == B.begin() || it1 == it2) continue;
        it2--;
        int l=it1-B.begin(), r=it2-B.begin();

        mi = 1e9;
        mi = min(mi, B[r]-A[i]);
        mi = min(mi, A[i+1]-B[l]);
        for (int j=l; j<r; j++) mi = min(mi, B[j]-A[i]+A[i+1]-B[j+1]);
        ans += mi;
    }

    ans += max(0, B[M-1] - A[N-1]);
    ans += max(0, A[0] - B[0]);

    cout << ans << endl;

    return 0;
}