#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define P pair<ll,ll>
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) (UB(A,x)-LB(A,x))
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
//using mint=modint1000000007;
using mint=modint998244353;
void chmax(ll&a,ll b){a=max(a,b);}
void chmin(ll&a,ll b){a=min(a,b);}
signed main(){
  ll N,M;cin>>N>>M;
  vector<ll>A(N);REP(i,N)cin>>A[i];
  vector<vector<ll>>B(N+1);
  REP(i,M){
    ll b;cin>>b;
    B[LB(A,b)].emplace_back(b);
  }
  ll ans=0;
  if(B[0].size())ans+=A[0]-B[0][0];
  if(B[N].size())ans+=B[N][B[N].size()-1]-A[N-1];
  FOR(i,1,N)if(B[i].size()){
    //A[i-1]とA[i]のはざま
    ll res=min(A[i]-B[i][0],B[i][B[i].size()-1]-A[i-1]);
    REP(j,B[i].size()-1)chmin(res,B[i][j]-A[i-1]+A[i]-B[i][j+1]);
    ans+=res;
  }
  cout<<ans<<endl;
  return 0;
}