#include<bits/stdc++.h>
using namespace std;
using ll = long long;
mt19937 rnd(time(NULL));
const int N=200010;
struct Info{
    int sum;int num;
    ll ans;
    int s1,n1,a1;int bm;
    Info(ll s=0,ll n=0,ll a=0,int b=0){
        sum=s,num=n;
        ans=a;s1=s,n1=n;a1=a;
        bm=b;
    };
    void print(){
        cerr<<sum<<' '<<num<<' '<<ans<<' '<<s1<<' '<<n1<<' '<<bm<<'\n';
    }
    bool operator<(const Info a)const {
        if(1ll*s1*a.n1!=1ll*a.s1*n1)    return 1ll*s1*a.n1<1ll*a.s1*n1;
        else return bm<a.bm;
    }
    bool operator<=(const Info a)const {
        if(1ll*s1*a.n1!=1ll*a.s1*n1)    return 1ll*s1*a.n1<1ll*a.s1*n1;
        else return bm<=a.bm;
    }
};
Info add(Info l,Info mid,Info r){
    Info res=mid;
    res.sum=l.sum+mid.s1+r.sum;res.num=l.num+mid.n1+r.num;
    res.ans=l.ans+mid.a1+r.ans+1ll*mid.s1*l.num+1ll*(l.num+mid.n1)*r.sum;
    return res;
}
struct treap{
    #define ls(x)   tr[x].l
    #define rs(x)   tr[x].r
    struct node{
        Info res;
        int l,r,rnd;
    }tr[N];
    int tot=0,rt=0;
    int intt(Info a){
        ++tot;int q=tot;
        ls(q)=rs(q)=0,tr[q].rnd=rnd();
        tr[q].res=a;
        return q;
    }
    void pushup(int p){
        tr[p].res=add(tr[ls(p)].res,tr[p].res,tr[rs(p)].res);
    }
    int merge(int p,int q){
        if(!p||!q)  return p|q;
        if(tr[p].rnd<=tr[q].rnd){
            tr[p].r=merge(tr[p].r,q);
            pushup(p);return p;
        }
        else{
            tr[q].l=merge(p,tr[q].l);
            pushup(q);return q;
        }
    }
    void split(int p,Info res,int& x,int& y,int t){
        if(!p)  {x=y=0;return ;}
        if((t==0?(tr[p].res<res):(tr[p].res<=res))){
            x=p;split(rs(p),res,rs(x),y,t);
        }
        else{
            y=p;split(ls(p),res,x,ls(y),t);
        }
        pushup(p);
    }
    array<int,3> split(Info x){
        int lo,ro,mid;
        split(rt,x,lo,ro,0);
        split(ro,x,mid,ro,1);
        return {lo,mid,ro};
    }
    void insert(Info a){
        auto [lo,mid,ro]=split(a);
        mid=intt(a);
        rt=merge(merge(lo,mid),ro);
    }
    void del(Info a){
        auto [lo,mid,ro]=split(a);
        assert(mid);
        rt=merge(lo,ro);
    }
    ll get_ans(){
        return tr[rt].res.ans;
    }
};
treap tp;
void solve(){
    int n,m;
    cin>>n>>m;
    vector<int> a(n);
    for(int i=0;i<n;i++)   cin>>a[i];
    sort(a.begin(),a.end());
    vector<int> b(n+2);
    for(int i=0;i<n;i++){
        if(i==0)    b[i+1]=a[i];
        else b[i+1]=a[i]-a[i-1];
    }
    b[n+1]=m+1-a[n-1];
    vector<ll> preb(n+2),segb(n+3);
    vector<int> pre(n+2);
    for(int i=1;i<=n+1;i++){
        preb[i]=preb[i-1]+1ll*b[i]*i;
    }
    for(int i=n+1;i>=1;i--){
        segb[i]=segb[i+1]+1ll*b[i]*(n+2-i);
    }
    for(int i=1;i<=n+1;i++){
        pre[i]=pre[i-1]+b[i];
    }
    auto getp=[&](int lo,int ro)->ll {
        return 2*(preb[ro]-preb[lo-1]-1ll*lo*(pre[ro]-pre[lo-1]))-1ll*(ro-lo)*(pre[ro]-pre[lo-1]);
    };
    auto gets=[&](int lo,int ro)->ll {
        return 2*(segb[lo]-segb[ro+1]-1ll*(n+2-ro)*(pre[ro]-pre[lo-1]))-1ll*(ro-lo)*(pre[ro]-pre[lo-1]);
    };
    vector<Info>  ad(n+2);
    vector<vector<Info>> dl(n+2);
    int bm=0;
    vector<Info> stk;
    for(int i=n+1;i>=1;i--){
        int lo=i,s1=b[i],n1=1;
        while(!stk.empty()){
            Info r=stk.back();
            if(1ll*r.s1*n1>=1ll*s1*r.n1) {s1+=r.s1,n1+=r.n1;dl[i].push_back(r);stk.pop_back();}
            else break;
        }
        int ro=lo+n1-1;
        Info w=Info(s1,n1,(gets(lo,ro)+1ll*s1*(n1+1))/2,++bm);
        stk.push_back(w);ad[i]=w; 
    }
    for(auto i:stk) tp.insert(i);
    stk.clear();
    ll ans=0;
    for(int i=1;i<=n+1;i++){
        tp.del(ad[i]);for(auto j:dl[i]) tp.insert(j);    
        if(i!=1){
            int ro=i-1,s1=b[i-1],n1=1;
            while(!stk.empty()){
                Info r=stk.back();
                if(1ll*r.s1*n1>=1ll*s1*r.n1) {s1+=r.s1,n1+=r.n1;tp.del(r);stk.pop_back();}
                else break;
            }
            int lo=ro-n1+1;
            Info w=Info(s1,n1,(getp(lo,ro)+1ll*s1*(n1+1))/2,++bm);tp.insert(w);
            stk.push_back(w); 
        }
        ans=max(ans,tp.get_ans()+1ll*n*b[i]);
        // cerr<<tp.get_ans()+n*b[i]<<'\n';
    }
    cout<<ans<<'\n';

}
int main(){
    ios::sync_with_stdio(0),cin.tie(0);
    int _ =1;
    // cin>>_;
    while(_--)  solve();

    return 0;
}

/*
3 10
3 7 10
*/

/*
5 20
3 10 11 14 17
*/