#include <bits/stdc++.h> using namespace std; typedef long long ll; vector<int>solve2(const vector<int>&v,int from){ vector<int>que; map<int,int>mp; for(int x=from;x<v.size();++x){ if(mp.find(v[x])==mp.end()){ que.emplace_back(v[x]); mp[v[x]]=que.size()-1; }else{ while(true){ int aback=que.back(); mp.erase(aback); que.pop_back(); if(aback==v[x])break; } } } return que; } vector<int> solve(int N,long long int K,vector<int>v,int start){ vector<int>rs(N); { map<int,int>mp; for(int i=N-1;i>=0;--i){ mp[v[i]]=N+i; } for(int i=N-1;i>=0;--i){ rs[i]=mp[v[i]]; mp[v[i]]=i; } } long long int ny=0,nx=start; map<int,long long int>mp; mp[start]=0; while(true){ //cout<<nx<<ny<<endl; auto next_x=rs[nx]; long long next_y=ny; //cout<<next_x<<' '<<next_y<<endl; if(next_x>=N){ next_y++; next_x-=N; } next_x++; if(next_x>=N){ next_y++; next_x-=N; } if(next_y>=K){ if(K-1==next_y){ v.insert(v.end(),v.begin(),v.end()); } return solve2(v,nx); }else{ ny=next_y; nx=next_x; if(mp.find(nx)==mp.end()){ mp[nx]=ny; }else{ long long sa=-(mp[nx]-ny); long long int rest=K-ny; rest%=sa; //cout<<rest<<endl; if(rest==0)rest=sa; long long xx=K%sa; if(xx==0)xx=sa; assert(nx==0); return solve(N,xx,v,0); } } } assert(false); } #define WHATS(var) cout<<#var<<"="<<var<<endl; int main() { ios::sync_with_stdio(false); int N,M;cin>>N>>M; set<long long int>sushis,teas; for(int i=0;i<N;++i){ int a;cin>>a; sushis.emplace(a); sushis.emplace(a+M); sushis.emplace(a+2*M); } for(int i=0;i<N;++i){ int a;cin>>a; teas.emplace(a); teas.emplace(a+M); teas.emplace(a+2*M); } long long int answer=0; int now=0; for(int i=0;i<N;++i){ auto it=sushis.lower_bound(now); answer+=*it-now; now=*it; now%=M; for(int j=0;j<3;++j){ sushis.erase(now+j*M); } auto jt=teas.lower_bound(now); auto lt=jt; if(!sushis.empty()){ auto kt=sushis.lower_bound(*jt); //WHATS(*kt); //WHATS(*teas.upper_bound(*kt)); //WHATS(*prev(teas.upper_bound(*kt))); lt=prev(teas.upper_bound(*kt)); } answer+=*lt-now; now=*lt; now%=M; for(int j=0;j<3;++j){ teas.erase(now+M*j); } } cout<<answer<<endl; return 0; }