#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(n); i++)



int main(){
    int N,M; cin >> N >> M;
    vector<i64> A(N);
    rep(i,N) cin >> A[i];
    vector<vector<i64>> B(A.size() + 1);
    rep(i,M){
        int b; cin >> b;
        int p = upper_bound(A.begin(), A.end(), b) - A.begin();
        B[p].push_back(b);
    }
    vector<i64> ans(B.size(), 0);
    rep(i,B.size()) if(!B[i].empty()) ans[i] = 1001001001;
    for(int i=0; i<A.size(); i++) if(!B[i].empty()) ans[i] = min(ans[i], A[i] - B[i].front());
    for(int i=0; i<A.size(); i++) if(!B[i+1].empty()) ans[i+1] = min(ans[i+1], B[i+1].back() - A[i]);
    for(int i=1; i<A.size(); i++) if(!B[i].empty()){
        i64 d = A[i] - A[i-1] - 1;
        for(int j=0; j+1 < B[i].size(); j++){
            ans[i] = min(ans[i], d - (B[i][j+1] - B[i][j] - 1));
        }
    }

    i64 finalans = 0;
    for(auto a : ans) finalans += a;
    cout << finalans << endl;
    return 0;
}




struct ios_do_not_sync {
    ios_do_not_sync() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} ios_do_not_sync_instance;