// 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; }