1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5
 6 int n,ans;
 7 int s[20005];
 8 int sa[20005],rk[20005];
 9 int tr[20005],h[20005];
10
11 int cmp(int x,int y,int k)
12 {
13     if(x+k>n||y+k>n)return 0;
14     return rk[x]==rk[y]&&rk[x+k]==rk[y+k];
15 }
16
17 void cal()
18 {
19     int i,cnt;
20     for(i=1;i<=n;i++)h[s[i]]++;
21     for(cnt=0,i=1;i<=200;i++)if(h[i])tr[i]=++cnt;
22     for(i=1;i<=200;i++)h[i]+=h[i-1];
23     for(i=1;i<=n;i++)rk[i]=tr[s[i]],sa[h[s[i]]--]=i;
24     for(int k=1;cnt!=n;k<<=1)
25     {
26         for(i=1;i<=n;i++)h[i]=0;
27         for(i=1;i<=n;i++)h[rk[i]]++;
28         for(i=1;i<=n;i++)h[i]+=h[i-1];
29         for(i=n;i;i--)if(sa[i]>k)tr[sa[i]-k]=h[rk[sa[i]-k]]--;
30         for(i=1;i<=k;i++)tr[n-i+1]=h[rk[n-i+1]]--;
31         for(i=1;i<=n;i++)sa[tr[i]]=i;
32         for(cnt=0,i=1;i<=n;i++)tr[sa[i]]=cmp(sa[i],sa[i-1],k)?cnt:++cnt;
33         for(i=1;i<=n;i++)rk[i]=tr[i];
34     }
35     for(i=1;i<=n;i++)h[i]=0;
36     for(i=1;i<=n;i++)
37     {
38         if(rk[i]==1)continue;
39         for(int j=max(1,h[rk[i-1]]-1);;j++)
40         {
41             if(s[i+j-1]==s[sa[rk[i]-1]+j-1])h[rk[i]]=j;
42             else break;
43         }
44     }
45 }
46
47 int check(int k)
48 {
49     if(k>n)return 0;
50     int l,r;
51     l=r=sa[1];
52     for(int i=2;i<=n;i++)
53     {
54         if(h[i]>=k)
55         {
56             l=min(l,sa[i]);
57             r=max(r,sa[i]);
58             if(r-l>k)return 1;
59         }else l=r=sa[i];
60     }
61     return 0;
62 }
63
64 int main()
65 {
66     scanf("%d",&n);
67     while(n)
68     {
69         memset(h,0,sizeof(h));
70         memset(tr,0,sizeof(tr));
71         memset(rk,0,sizeof(rk));
72         memset(sa,0,sizeof(sa));
73         ans=0;
74         for(int i=1;i<=n;i++)scanf("%d",&s[i]);
75         for(int i=1;i<n;i++)s[i]=s[i+1]-s[i]+90;
76         cal();
77         for(int i=20;i>=0;i--)
78             if(check(ans|(1<<i)))ans|=(1<<i);
79         ans=(ans+1)>=5?(ans+1):0;
80         printf("%d\n",ans);
81         scanf("%d",&n);
82     }
83     return 0;
84 }