1 //
 2 //by coolxxx
 3 //#include<bits/stdc++.h>
 4 #include<iostream>
 5 #include<algorithm>
 6 #include<string>
 7 #include<iomanip>
 8 #include<map>
 9 #include<stack>
10 #include<queue>
11 #include<set>
12 #include<bitset>
13 #include<memory.h>
14 #include<time.h>
15 #include<stdio.h>
16 #include<stdlib.h>
17 #include<string.h>
18 //#include<stdbool.h>
19 #include<math.h>
20 #define min(a,b) ((a)<(b)?(a):(b))
21 #define max(a,b) ((a)>(b)?(a):(b))
22 #define abs(a) ((a)>0?(a):(-(a)))
23 #define lowbit(a) (a&(-a))
24 #define sqr(a) ((a)*(a))
25 #define swap(a,b) ((a)^=(b),(b)^=(a),(a)^=(b))
26 #define mem(a,b) memset(a,b,sizeof(a))
27 #define eps (1e-8)
28 #define J 10
29 #define mod 1000000007
30 #define MAX 0x7f7f7f7f
31 #define PI 3.14159265358979323
32 #define N 100004
33 using namespace std;
34 typedef long long LL;
35 int cas,cass;
36 int n,m,lll,ans;
37 LL aans;
38 LL a[N],sum[N],l[N],r[N];
39 bool judge(LL h)
40 {
41     int i,j;
42     mem(l,0);mem(r,0x7f);
43     for(i=1;i<=n;i++)
44         if(i+h-a[i]<=n)l[i+h-a[i]]=i;//i往右每次+1扩展达到H时的位置为j=i+h[i]-a[i]，则L[j]即为i
45     for(i=n;i;i--)
46         if(i-h+a[i]>0)r[i-h+a[i]]=i;//同上，i往左每次+1扩展
47     for(i=1;i<=n;i++)l[i]=max(l[i],l[i-1]);//有可能在下降的过程中遇到比预期高度更高的，需要改为在更高的位置停止
48     for(i=n;i;i--)r[i]=min(r[i],r[i+1]);//比如当前高度是3，下一个高度是5,最终肯定是在5停下来而不是3
49     for(i=1;i<=n;i++)
50     {
51         if(l[i]==0 || r[i]==r[N-1])continue;
52         aans=1LL*(a[l[i]]+h)*(i-l[i]+1)/2;
53         aans+=1LL*(a[r[i]]+h-1)*(r[i]-i)/2;
54         aans-=sum[r[i]]-sum[l[i]-1];
55         if(aans<=m)return 1;
56     }
57     return 0;
58 }
59 int main()
60 {
61     #ifndef ONLINE_JUDGE
62 //    freopen("1.txt","r",stdin);
63 //    freopen("2.txt","w",stdout);
64     #endif
65     int i,j,k;
66     LL l,r,mid;
67 //    for(scanf("%d",&cass);cass;cass--)
68 //    for(scanf("%d",&cas),cass=1;cass<=cas;cass++)
69 //    while(~scanf("%s",s+1))
70     while(~scanf("%d",&n))
71     {
72         scanf("%d",&m);
73         sum[0]=0;l=0;
74         for(i=1;i<=n;i++)
75         {
76             scanf("%I64d",&a[i]);
77             sum[i]=sum[i-1]+a[i];
78             l=max(l,a[i]);
79         }
80         r=2000000000;
81         while(l<r)
82         {
83             mid=(l+r+1)>>1;
84             if(judge(mid))l=mid;
85             else r=mid-1;
86         }
87         printf("%I64d\n",r);
88     }
89     return 0;
90 }
91 /*
92 //
93
94 //
95 */