#include<iostream>
#include<algorithm>
#include<cassert>
using namespace std;
int N,M;
int A[2<<17],B[2<<17];
long long D[2<<17],UP[2<<17],DOWN[2<<17];
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin>>N>>M;
	for(int i=0;i<N;i++)cin>>A[i];
	for(int i=0;i<N;i++)cin>>B[i];
	for(int i=0;i<N;i++)
	{
		int d=B[i]-A[i];
		d%=M;
		if(d<0)d+=M;
		D[i+1]=d;
	}
	long long base=0;
	for(int i=1;i<=N+1;i++)
	{
		long long now=abs(D[i]-D[i-1]);
		base+=now;
		UP[i-1]=abs(D[i]+M-D[i-1])-now;
		DOWN[i-1]=abs(D[i]-M-D[i-1])-now;
	}
	sort(UP,UP+N+1);
	sort(DOWN,DOWN+N+1);
	long long ans=base;
	for(int c=1;c<=(N+1)/2;c++)
	{
		base+=UP[c-1];
		base+=DOWN[c-1];
		ans=min(ans,base);
	}
	cout<<ans/2<<endl;
}