Bear and Three Balls

题意翻译

Limak是一只小北极熊。他有N个球，我的第i个球的大小是T[i]。 Limak想给他的三个朋友每人一个球。 但是赠送礼物并不容易——莱马克必须遵守两条规则才能使朋友快乐： 没有两个朋友能得到同样大小的球。 没有两个朋友能得到大小超过2个2的球。 例如，Limak可以选择大小为4,5和3的球，或者大小为90,91和92的球。但他不能选择大小为5,5和6的球(两个朋友会得到同样大小的球),他不能选择大小为 30,31和33的球(因为尺寸30和33相差超过2)。 你的任务是检查Limak是否可以选择满足以上条件的三个球。 感谢@something 提供的翻译

题目描述

Limak is a little polar bear. He has $ n $ balls, the $ i $ -th ball has size $ t_{i} $ . Limak wants to give one ball to each of his three friends. Giving gifts isn't easy — there are two rules Limak must obey to make friends happy: - No two friends can get balls of the same size. - No two friends can get balls of sizes that differ by more than $ 2 $ . For example, Limak can choose balls with sizes $ 4 $ , $ 5 $ and $ 3 $ , or balls with sizes $ 90 $ , $ 91 $ and $ 92 $ . But he can't choose balls with sizes $ 5 $ , $ 5 $ and $ 6 $ (two friends would get balls of the same size), and he can't choose balls with sizes $ 30 $ , $ 31 $ and $ 33 $ (because sizes $ 30 $ and $ 33 $ differ by more than $ 2 $ ). Your task is to check whether Limak can choose three balls that satisfy conditions above.

输入输出格式

输入格式

The first line of the input contains one integer $ n $ ( $ 3<=n<=50 $ ) — the number of balls Limak has. The second line contains $ n $ integers $ t_{1},t_{2},...,t_{n} $ ( $ 1<=t_{i}<=1000 $ ) where $ t_{i} $ denotes the size of the $ i $ -th ball.

输出格式

Print "YES" (without quotes) if Limak can choose three balls of distinct sizes, such that any two of them differ by no more than $ 2 $ . Otherwise, print "NO" (without quotes).

输入输出样例

输入样例 #1

4
18 55 16 17

输出样例 #1

YES

输入样例 #2

6
40 41 43 44 44 44

输出样例 #2

NO

输入样例 #3

8
5 972 3 4 1 4 970 971

输出样例 #3

YES

说明

In the first sample, there are $ 4 $ balls and Limak is able to choose three of them to satisfy the rules. He must must choose balls with sizes $ 18 $ , $ 16 $ and $ 17 $ . In the second sample, there is no way to give gifts to three friends without breaking the rules. In the third sample, there is even more than one way to choose balls: 1. Choose balls with sizes $ 3 $ , $ 4 $ and $ 5 $ . 2. Choose balls with sizes $ 972 $ , $ 970 $ , $ 971 $ .