Best anime battles

#include<bits/stdc++.h>
using namespace std;
#define forx(x1,y1) for(unsigned long long x1=0;x1<y1;++x1)
#define INF 1e9
#define all(x2) begin(x2),end(x2)
#define size(t) ((ld)(t.size()))
#define last(x) (*(x.end()-1))
using ll= long long;
using ld= long double;
using ull=unsigned long long;
/*cout.setf(ios::fixed);
    cout.precision(6);*/
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    ll n,q;
    cin>>n>>q;
    vector<ll>v(n),m(q);
    forx(i,n)
        cin>>v[i];
    forx(i,q)
        cin>>m[i];
    stable_sort(all(v));
    stable_sort(all(m));
    ll res=0;
    auto a=lower_bound(all(m),v[0]);
    auto b=a;
    if(a!=m.begin()){
        if(abs(v[0]-*(--b))<abs(v[0]-*(a)))
            a=b;
    }
    res+=abs(v[0]-*(a));
    for(ll i=1;i<size(v)-1;i+=2)
        res+=abs(v[i]-v[i+1]);
    ll num=res;
    for(ll i=1;i<size(v);++i){
        if(i%2==1){
            num-=abs(v[i]-v[i+1]);
            num-=abs(v[i-1]-*a);
            num+=abs(v[i-1]-v[i+1]);
            a=lower_bound(all(m),v[i]);
            b=a;
            if(a!=m.begin()){
                if(abs(v[i]-*(--b))<abs(v[i]-*(a)))
                    a=b;
            }
            num+=abs(v[i]-*a);
        }
        else{
            num-=abs(v[i-1]-*a);
            num-=abs(v[i]-v[i-2]);
            num+=abs(v[i-1]-v[i-2]);
            a=lower_bound(all(m),v[i]);
            b=a;
            if(a!=m.begin()){
                if(abs(v[i]-*(--b))<abs(v[i]-*(a)))
                    a=b;
            }
            num+=abs(v[i]-*a);
        }
        if(num<res)
            res=num;
    }
    cout<<res;
}