#include<cstdio>

#include<cstring>

#include<algorithm>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PII pair<int, int>

#define PLI pair<LL, int>

#define PDD pair<double,double>

#define ull unsigned long long

using namespace std;

const int N =  + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const int base = ;

int n;

int s[N], a[N];

struct SuffixAutomaton {

    int last, cur, cnt, ch[N<<][], id[N<<], fa[N<<], dis[N<<], sz[N<<], c[N];

    int mx[N<<], mn[N<<];

    SuffixAutomaton() {cur = cnt = ;}

    void init() {

        for(int i = ; i <= cnt; i++) {

            memset(ch[i], , sizeof(ch[i]));

            sz[i] = c[i] = dis[i] = fa[i] = ;

        }

        cur = cnt = ;

    }

    void extend(int c, int id) {

        last = cur; cur = ++cnt;

        int p = last; dis[cur] = id;

        for(; p && !ch[p][c]; p = fa[p]) ch[p][c] = cur;

        if(!p) fa[cur] = ;

        else {

            int q = ch[p][c];

            if(dis[q] == dis[p]+) fa[cur] = q;

            else {

                int nt = ++cnt; dis[nt] = dis[p]+;

                memcpy(ch[nt], ch[q], sizeof(ch[q]));

                fa[nt] = fa[q]; fa[q] = fa[cur] = nt;

                for(; ch[p][c]==q; p=fa[p]) ch[p][c] = nt;

            }

        }

        sz[cur] = ;

    }

    void getSize(int n) {

        for(int i = ; i <= cnt; i++) c[dis[i]]++;

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

        for(int i = cnt; i >= ; i--) id[c[dis[i]]--] = i;

        for(int i = cnt; i >= ; i--) {

            int p = id[i];

            sz[fa[p]] += sz[p];

        }

    }

    void solve(int *s, int n) {

        memset(mx, , sizeof(int)*(cnt+));

        memset(mn, inf, sizeof(int)*(cnt+));

        for(int i = , p = ; i <= n; i++) {

            p = ch[p][s[i]];

            mx[p] = mn[p] = i;

        }

        for(int i = cnt; i >= ; i--) {

            int p = id[i];

            mx[fa[p]] = max(mx[fa[p]], mx[p]);

            mn[fa[p]] = min(mn[fa[p]], mn[p]);

        }

        int ans = ;

        for(int i = ; i <= cnt; i++) {

            ans = max(ans, min(mx[i]-mn[i], dis[i]));

        }

        if(ans < ) puts("");

        else printf("%d\n", ans+);

    }

} sam;

int main() {

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

        sam.init();

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

        for(int i = ; i < n; i++) s[i] = a[i+]-a[i]+base;

        for(int i = ; i < n; i++) sam.extend(s[i], i);

        sam.getSize(n-);

        sam.solve(s, n-);

    }

    return ;

}

/*

*/