#include<bits/stdc++.h>
using namespace std;
using ll=__int128;
const int N=2e5;
int n,m;
ll a[N+5];
ll ans;
struct val{
    ll s,ss; int c;
    val(ll s=0,ll ss=0,int c=0):s(s),ss(ss),c(c){}
    bool operator < (const val t) const{
        return s*t.c==t.s*c?c<t.c:s*t.c<t.s*c;
    }
}st1[N+5],st2[N+5];
int s1,s2;
val xx[N*2+5];
int xs;
vector<val> op[N+5];
val merge(val x,val y){
    // printf("x %lld %lld %d\n",x.s,x.ss,x.c);
    // printf("y %lld %lld %d\n",y.s,y.ss,y.c);
    x.ss+=y.ss+x.s*y.c;
    x.s+=y.s; x.c+=y.c;
    // printf("res %lld %lld %d\n",x.s,x.ss,x.c);
    // printf("%lld %lld %d\n",x.s,x.ss,x.c);
    return x;
}
void prep(){
    for(int i=1;i<=n;i++){
        val tmp=val(a[i],a[i],1);
        while(s1&&tmp<st1[s1]){
            tmp=merge(tmp,st1[s1]);
            s1--;
        }
        st1[++s1]=tmp;
        xx[++xs]=tmp;
    }
    for(int i=n;i;i--){
        val tmp=val(a[i],a[i],1);
        while(s2&&tmp<st2[s2]){
            op[i].push_back(st2[s2]);
            tmp=merge(tmp,st2[s2]);
            s2--;
        }
        st2[++s2]=tmp;
        xx[++xs]=tmp;
    }
    sort(xx+1,xx+1+xs);
}
struct Segtr{
    val tr[N*8+5];
    #define lc id<<1
    #define rc id<<1|1
    void push_up(int id){
        tr[id]=merge(tr[lc],tr[rc]);
    }
    void add(int l,int r,int p,int x,int id){
        if(l==r){
            if(x>0){
                tr[id].s+=xx[l].s;
                tr[id].c+=xx[l].c;
            }
            else{
                tr[id].s-=xx[l].s;
                tr[id].c-=xx[l].c;
            }
            return;
        }
        int mid=l+r>>1;
        if(p<=mid) add(l,mid,p,x,lc);
        else add(mid+1,r,p,x,rc);
        push_up(id);
    }
    val query(int l,int r,int st,int en,int id){
        if(st>en) return val();
        if(st<=l&&en>=r) return tr[id];
        int mid=l+r>>1; val ans;
        if(st<=mid) ans=merge(ans,query(l,mid,st,en,lc));
        if(en>mid) ans=merge(ans,query(mid+1,r,st,en,rc));
        return ans;
    }
}T;
int find(val x){
    int l=1,r=xs;
    while(l<=r){
        int mid=l+r>>1;
        if(x<xx[mid]) r=mid-1;
        else l=mid+1;
    }
    return r;
}
ll ins(val it){
    int pos=find(it);
    val vl=T.query(1,xs,1,pos-1,1),vr=T.query(1,xs,pos,xs,1);
    T.add(1,xs,pos,1,1);
    return it.s*(n-1-vl.c)-it.ss-vr.s*it.c;
}
ll del(val it){
    int pos=find(it);
    T.add(1,xs,pos,-1,1);
    val vl=T.query(1,xs,1,pos-1,1),vr=T.query(1,xs,pos,xs,1);
    return it.s*(n-1-vl.c)-it.ss-vr.s*it.c;
}
int main(){
    scanf("%d %d",&n,&m); m++;
    for(int i=1;i<=n;i++)
        scanf("%lld",&a[i]);
    sort(a+1,a+1+n);
    a[++n]=m;
    for(int i=n;i;i--) a[i]-=a[i-1];
    prep();
    // fprintf(stderr,"prep\n");
    ll res=0;
    for(int i=1;i<=s2;i++){
        // fprintf(stderr,"%lld %lld %d\n",st2[i].s,st2[i].ss,st2[i].c);
        res+=ins(st2[i]);
    }
    s1=0;
    // fprintf(stderr,"prep\n");
    for(int i=1;i<=n;i++){
        res-=del(st2[s2]); s2--;
        for(auto it:op[i]){
            res+=ins(it);
            st2[++s2]=it;
        }
        ans=max(ans,1ll*m*(n-1)-res);
        // printf("%lld\n",res);
        val tmp=val(a[i],a[i],1);
        while(s1&&tmp<st1[s1]){
            res-=del(st1[s1]);
            tmp=merge(tmp,st1[s1]);
            s1--;
        }
        res+=ins(tmp);
        st1[++s1]=tmp;
    }
    // printf("lstc %d\n",T.tr[1].c);
    // for(int i=1;i<=s1;i++){
    //     printf("%lld %lld %d\n",st1[i].s,st1[i].ss,st1[i].c);
    // }
    printf("%lld\n",(long long)ans);
    return 0;
}