#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <ctime>#include <cassert>#include <iostream>#include <sstream>#include <map>#include <set>#include <vector>#include <queue>#include <algorithm>#include <iomanip>using namespace std;#define max(x,y) ((x)>(y)?(x):(y))#define min(x,y) ((x)<(y)?(x):(y))#define abs(x) ((x)>=0?(x):-(x))#define i64 long long#define u32 unsigned int#define u64 unsigned long long#define clr(x,y) memset(x,y,sizeof(x))#define PI acos(-1.0)#define lowbit(x) (x&(-x))#define sqr(x) ((x)*(x))#define LL long long#define N 3003int n;short dp[N][N];int path[N];LL a[N];int pos[N];int b[N];struct treearray{ int f[N + 100]; void init() { memset(f,0,sizeof(f)); } void update(int x,int val) { while( x <= N ) { f[x] += val; x += lowbit(x); } } int query(int x) { int res; res = 0 ; while(x > 0 ) { res += f[x]; x -= lowbit(x); } return res; } int getp(int x) { return query(x) - query(x-1); } void up1(int x,int val) { update(x,val-getp(x)); }};treearray ta;int main(){ int n1; int flag = 0; while (scanf("%d",&n)==1){ if (flag) puts(""); flag = 1; for (int i=0;i<n;i++) scanf("%lld",&a[i]); if (n == 1){ printf("1n"); printf("%lldn",a[0]); continue; } memset(dp,0,sizeof(dp)); int ans = 0; int ansi,ansj; ta.init(); for(int i = 0; i < n ; i++ ) b[i] = a[i]; sort(b,b+n); n1 = unique(b,b+n) - b; for(int i = 0 ; i < n ; i ++ ) pos[i] = lower_bound(b,b+n1,a[i]) - b + 1 ; for (int j=0;j<n;j++) { for (int i=j+1;i<n;i++){ int x = a[i] - a[j]; int k; int p = lower_bound(b,b+n1,x) - b ; if(b[p] != x) k = -1; else { p = p + 1; int tmp = ta.getp(p); if(tmp == 0 ) { k = -1; } else k= tmp - 1; } if (k!=-1){ dp[i][j] = dp[j][k] + 1; }else{ dp[i][j] = 2; } if (dp[i][j] > ans){ ans = dp[i][j]; ansi = i; ansj = j; } } ta.up1(pos[j],j+1); } printf("%dn",ans); int tot = 0; path[++tot] = ansi; path[++tot] = ansj; while (tot < ans){ int x = a[ansi] - a[ansj]; int k; for (k=0;k<ansj;k++){ if (a[k] == x && dp[ansj][k] + 1 == dp[ansi][ansj]){ break; } } if (k < ansj){ path[++tot] = k; ansi = ansj; ansj = k; }else break; } for (int i=1;i<ans;i++) printf("%lld ",a[path[ans-i+1]]); printf("%lldn",a[path[1]]); }return 0;}
