#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>using namespace std;#define N 20004int s[N], f[N];int n, sa[N], height[N], rank[N], tmp[N], top[N];void makesa(){ int i, j, len, na; na = (n <256?256 : n); memset(top, 0, na *sizeof(int)); for (i =0; i < n; i++) top[rank[i] = s[i] &0xff]++; for (i =1; i < na; i++) top[i] += top[i -1]; for (i =0; i < n; i++) sa[--top[rank[i]]] = i; for (len =1; len < n; len <<=1) { for (i =0; i < n; i++) { j = sa[i] - len; if (j <0) j += n; tmp[top[rank[j]]++] = j; } sa[tmp[top[0] =0]] = j =0; for (i =1; i < n; i++) { if (rank[tmp[i]] != rank[tmp[i -1]] || rank[tmp[i] + len] != rank[tmp[i -1] + len]) top[++j] = i; sa[tmp[i]] = j; } memcpy(rank, sa, n *sizeof(int)); memcpy(sa, tmp, n *sizeof(int)); if (j >= n -1) break; }}void lcp(){ int i, j, k; for (j = rank[height[i = k =0] =0]; i < n -1; i++, k++) while (k >=0&& s[i] != s[sa[j -1] + k]) height[j] = (k--), j = rank[sa[j] +1];}bool ok(int d){ int l = sa[0], r = sa[0]; for (int i =0; i < n; i++) { if (height[i] < d) { l = sa[i]; r = sa[i]; continue; } if (sa[i] < l) l = sa[i]; if (sa[i] > r) r = sa[i]; if (r - l > d) return true; } return false;}int binarysearch(){ int l =0; int r = n; while (l < r) { int mid = (l + r) /2+ ((l + r) &1); if (ok(mid)) l = mid; else r = mid -1; } return l;}int main(){ while (scanf("%d", &n), n) { for (int i =0; i < n; i++) scanf("%d", &f[i]); for (int i =0; i < n -1; i++) s[i] = f[i +1] - f[i]; makesa(); lcp(); int ans = binarysearch(); if (ans >=4) printf("%dn", ans +1); else printf("0n"); } return 0;}
