// https://atcoder.jp/contests/tkppc6-1/tasks/tkppc6_1_k

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005;
const ll INF=1LL<<60;
int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N;cin>>N;
    ll M;cin>>M;
    vector<ll> A(N+2);
    for(int i=1;i<=N;i++) cin>>A[i];
    for(int i=1;i<=N;i++){
        ll x;cin>>x;
        A[i]=x-A[i];
        if(A[i]<0) A[i]+=M;
    }
    vector<ll> S(N+1);
    ll sum=0;
    for(int i=1;i<=N+1;i++){
        S[i-1]=(A[i]-A[i-1]+M)%M;
        sum+=S[i-1];
    }
    sort(all(S));
    
    ll ans=0;
    for(int i=0;i<N+1-sum/M;i++) ans+=S[i];
    cout<<ans<<endl;
}