#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll a[2000005],pre[2000005];
int read(){
	int x=0;
	char c=getchar();
	while(c<'0' || c>'9')c=getchar();
	while(c>='0' && c<='9'){
		x=x*10+c-48;
		c=getchar();
	}
	return x;
}
int n;
ll m;
int main(){
	n=read();m=read();
	for(int i=1;i<=n;i++)a[i]=read();
	sort(a+1,a+n+1);
	for(int i=n+1;i<=n+n;i++)a[i]=a[i-n]+m;
	for(int i=1;i<=n+n;i++)pre[i]=pre[i-1]+a[i];
	int L=1,R=n,mid=(n+1)/2;
	int lenl=mid-L+1,lenr=R-mid;
	ll ans=0x3f3f3f3f3f3f3f3f;
	while(R<=n+n){
		ans=min(ans,(a[mid]+a[mid]-lenl+1)*lenl/2-(pre[mid]-pre[L-1])+pre[R]-pre[mid]-(a[mid]+1+a[mid]+lenr)*lenr/2);
		L++;R++;mid++;
	}
	printf("%lld",ans);
	return 0;
	//quod erat demonstrandum
}