1 #include <bits/stdc++.h>
2 using namespace std;
3
4 #define LS 2*i
5 #define RS 2*i+1
6 #define UP(i,x,y) for(i=x;i<=y;i++)
7 #define DOWN(i,x,y) for(i=x;i>=y;i--)
8 #define MEM(a,x) memset(a,x,sizeof(a))
9 #define W(a) while(a)
10 #define gcd(a,b) __gcd(a,b)
11 #define LL long long
12 #define N 20005
13 #define MOD 1000000007
14 #define INF 0x3f3f3f3f
15 #define EXP 1e-8
16 int wa[N],wb[N],wsf[N],wv[N],sa[N];
17 int rank1[N],height[N],s[N],a[N],n;
18 char str1[N],str2[N];
19 //sa:字典序中排第i位的起始位置在str中第sa[i]
20 //rank:就是str第i个位置的后缀是在字典序排第几
21 //height：字典序排i和i-1的后缀的最长公共前缀
22 int cmp(int *r,int a,int b,int k)
23 {
24 return r[a]==r[b]&&r[a+k]==r[b+k];
25 }
26 void getsa(int *r,int *sa,int n,int m)//n要包含末尾添加的0
27 {
28 int i,j,p,*x=wa,*y=wb,*t;
29 for(i=0; i<m; i++) wsf[i]=0;
30 for(i=0; i<n; i++) wsf[x[i]=r[i]]++;
31 for(i=1; i<m; i++) wsf[i]+=wsf[i-1];
32 for(i=n-1; i>=0; i--) sa[--wsf[x[i]]]=i;
33 p=1;
34 j=1;
35 for(; p<n; j*=2,m=p)
36 {
37 for(p=0,i=n-j; i<n; i++) y[p++]=i;
38 for(i=0; i<n; i++) if(sa[i]>=j) y[p++]=sa[i]-j;
39 for(i=0; i<n; i++) wv[i]=x[y[i]];
40 for(i=0; i<m; i++) wsf[i]=0;
41 for(i=0; i<n; i++) wsf[wv[i]]++;
42 for(i=1; i<m; i++) wsf[i]+=wsf[i-1];
43 for(i=n-1; i>=0; i--) sa[--wsf[wv[i]]]=y[i];
44 t=x;
45 x=y;
46 y=t;
47 x[sa[0]]=0;
48 for(p=1,i=1; i<n; i++)
49 x[sa[i]]=cmp(y,sa[i-1],sa[i],j)? p-1:p++;
50 }
51 }
52 void getheight(int *r,int n)//n不保存最后的0
53 {
54 int i,j,k=0;
55 for(i=1; i<=n; i++) rank1[sa[i]]=i;
56 for(i=0; i<n; i++)
57 {
58 if(k)
59 k--;
60 else
61 k=0;
62 j=sa[rank1[i]-1];
63 while(r[i+k]==r[j+k])
64 k++;
65 height[rank1[i]]=k;
66 }
67 }
68 int ans;
69 int fun(int k)
70 {
71 int i,maxn,minn;
72 maxn = minn = sa[1];
73 UP(i,2,n)
74 {
75 if(height[i]>=k && i<n)
76 {
77 minn = min(minn,sa[i]);
78 maxn = max(maxn,sa[i]);
79 continue;
80 }
81 if(maxn-minn>=k) return 1;
82 maxn = minn = sa[i];
83 }
84 return 0;
85 }
86
87
88 int main()
89 {
90 int i,j,k;
91 W((~scanf("%d",&n),n))
92 {
93 UP(i,0,n-1)
94 {
95 scanf("%d",&s[i]);
96 }
97 UP(i,0,n-2)
98 {
99 s[i] = s[i+1]-s[i]+100;
100 }
101 s[--n] = 0;
102 getsa(s,sa,n+1,200);
103 getheight(s,n);
104 int l = 4,r = n;
105 W(l<=r)
106 {
107 int mid = (l+r)/2;
108 if(fun(mid))
109 {
110 ans = mid;
111 l=mid+1;
112 }
113 else r = mid-1;
114 }
115 ans++;
116 printf("%d\n",ans<5?0:ans);
117 }
118
119 return 0;
120 }
