poj1743

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<cstring>

using namespace std;

int x,n,i,xzq,mm;
int a[20011],rank[20011],sa[20011],h[20011],b[20011];
int co[20011],nr[20011],s[20011];

void sort(int *a)
{
    int i,mn;
    if(mm>n)mn=mm;
    else mn=n;
    for(i=0;i<=mn;i++)co[i]=0;
    for(i=1;i<=n;i++)co[a[i]+1]++;
    for(i=1;i<=mn;i++)co[i]+=co[i-1];
    for(i=1;i<=n;i++)nr[i]=0;
    for(i=1;i<=n;i++){
        co[a[sa[i]]]++;
        nr[co[a[sa[i]]]]=sa[i];
    }
    for(i=1;i<=n;i++)sa[i]=nr[i];
}

void getrank()
{
    int i;
    x=0;
    for(i=1;i<=n;i++){
        if(i==1||a[sa[i]]!=a[sa[i-1]]||b[sa[i]]!=b[sa[i-1]])x++;
        rank[sa[i]]=x;
    }
}

void Suffix()
{
    int i,l,last,j,k;
    for(i=1;i<=n;i++){
        sa[i]=i;
        b[i]=0;
    }
    sort(a);
    getrank();
    l=1;
    while(x!=n){
        for(i=1;i<=n;i++){
            a[i]=rank[i];
            if(i+l<=n)b[i]=rank[i+l];
            else b[i]=0;
        }
        sort(b);
        sort(a);
        getrank();
        l*=2;
    }
    last=0;
    for(i=1;i<=n;i++){
        if(last)last--;
        if(rank[i]==1)continue;
        j=i;
        k=sa[rank[i]-1];
        while(j+last<=n&&k+last<=n&&s[j+last]==s[k+last])last++;
        h[rank[i]]=last;
    }
}

bool check(int x)
{
    int i,minn,maxn;
    minn=2147483647;
    maxn=0;
    for(i=2;i<=n+1;i++){
        if(sa[i-1]<minn)minn=sa[i-1];
        if(sa[i-1]>maxn)maxn=sa[i-1];
        if(h[i]<x){
            if(maxn-minn>x)return true;//（必须是严格大于，这就是之前说的那个特判）
            maxn=0;
            minn=2147483647;
        }
    }
    return false;
}

void Work()
{
    int l,r,mid;
    l=1;
    r=n;
    while(l<=r){
        mid=(l+r)/2;
        if(check(mid))l=mid+1;
        else r=mid-1;
    }
    xzq=r;
}

int main()
{
    while(true){
        scanf("%d",&n);
        if(n==0)break;
        memset(sa,0,sizeof(sa));
        memset(h,0,sizeof(h));
        memset(rank,0,sizeof(rank));
        for(i=1;i<=n;i++)scanf("%d",&a[i]);
        mm=0;
        for(i=1;i<n;i++){
            a[i]=a[i+1]-a[i]+100;
            if(a[i]>mm)mm=a[i];
            s[i]=a[i];
        }
        mm++;
        n--;
        a[n]=0;
        Suffix();
        Work();
        xzq++;
        if(xzq<5)printf("0\n");
        else printf("%d\n",xzq);
    }
}