Description：

Solution：

Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<cctype>

#include<cstring>

using namespace std;

int n;

#define MAXN 40010

int h[MAXN],s[MAXN],s_[MAXN];

int sa[MAXN],rnk[MAXN],c1[MAXN],c2[MAXN],height[MAXN];

int c[MAXN];

void make_SA(int n,int m)

{

	int p = 0;

	int *x = c1,*y = c2;

	for(int i = 1;i <= m;++i)c[i] = 0;

	for(int i = 1;i <= n;++i)++c[x[i] = s[i]];

	for(int i = 1;i <= m;++i)c[i] += c[i - 1];

	for(int i = n;i >= 1;--i)sa[c[x[i]]--] = i;

	for(int k = 1;k <= n;k = k << 1)

	{

		p = 0;

		for(int i = n - k + 1;i <= n;++i)y[++p] = i;

		for(int i = 1;i <= n;++i)if(sa[i] > k)y[++p] = sa[i] - k;

		for(int i = 1;i <= m;++i)c[i] = 0;

		for(int i = 1;i <= n;++i)++c[x[y[i]]];

		for(int i = 1;i <= m;++i)c[i] += c[i - 1];

		for(int i = n;i >= 1;--i)sa[c[x[y[i]]]--] = y[i];

		p = 1;

		swap(x,y);

		x[sa[1]] = 1;

		for(int i = 2;i <= n;++i)

		{

			x[sa[i]] = (y[sa[i]] == y[sa[i - 1]] && y[sa[i] + k] == y[sa[i - 1] + k] ? p : ++p);

		}

		if(p >= n)break;

		m = p;

	}

	for(int i = 1;i <= n;++i)rnk[sa[i]] = i;

	int k = 0;

	for(int i = 1;i <= n;++i)

	{

		if(rnk[i] == 1)continue;

		if(k)--k;

		int j = sa[rnk[i] - 1];

		while(j + k <= n && i + k <= n && s[i + k] == s[j + k])++k;

		height[rnk[i]] = k;

	}

	return;

}

bool check(int v)

{

	int maxv = 0xc0c0c0c0,minv = 0x3f3f3f3f;

	for(int i = 1;i <= n;++i)

	{

		if(height[i] < v)

		{

			maxv = sa[i];minv = sa[i];

			continue;

		}

		else

		{

			maxv = max(maxv,sa[i]);

			minv = min(minv,sa[i]);

			if(maxv - sa[i] > v || sa[i] - minv > v)

			{

				return true;

			}

		}

	}

	return false;

}

int main()

{

	while(scanf("%d",&n) && n != 0)

	{

		for(int i = 1;i <= n;++i)scanf("%d",&h[i]);

		--n;

		for(int i = 1;i <= n;++i)s_[i] = s[i] = h[i + 1] - h[i];

		sort(s_ + 1,s_ + 1 + n);

		s_[0] = unique(s_ + 1,s_ + 1 + n) - s_ - 1;

		for(int i = 1;i <= n;++i)s[i] = lower_bound(s_ + 1,s_ + 1 + s_[0],s[i]) - s_;

		make_SA(n,s_[0]);

		int l = 0,r = n,mid;

		while(l < r)

		{

			mid = ((l + r + 1) >> 1);

			if(check(mid))l = mid;

			else r = mid - 1;

		}

		if(l >= 4)cout << l + 1 << endl;

		else cout << 0 << endl;

	}

	return 0;

}