Please subscribe to the official Codeforces channel in Telegram via the link: https://t.me/codeforces_official.
×

Virtual contest is a way to take part in past contest, as close as possible to participation on time. It is supported only ACM-ICPC mode for virtual contests.
If you've seen these problems, a virtual contest is not for you - solve these problems in the archive.
If you just want to solve some problem from a contest, a virtual contest is not for you - solve this problem in the archive.
Never use someone else's code, read the tutorials or communicate with other person during a virtual contest.

No tag edit access

E. Triple Flips

time limit per test

1 secondmemory limit per test

256 megabytesinput

standard inputoutput

standard outputYou are given an array $$$a$$$ of length $$$n$$$ that consists of zeros and ones.

You can perform the following operation multiple times. The operation consists of two steps:

- Choose three integers $$$1 \le x < y < z \le n$$$, that form an arithmetic progression ($$$y - x = z - y$$$).
- Flip the values $$$a_x, a_y, a_z$$$ (i.e. change $$$1$$$ to $$$0$$$, change $$$0$$$ to $$$1$$$).

Determine if it is possible to make all elements of the array equal to zero. If yes, print the operations that lead the the all-zero state. Your solution should not contain more than $$$(\lfloor \frac{n}{3} \rfloor + 12)$$$ operations. Here $$$\lfloor q \rfloor$$$ denotes the number $$$q$$$ rounded down. We can show that it is possible to make all elements equal to zero in no more than this number of operations whenever it is possible to do so at all.

Input

The first line contains a single integer $$$n$$$ ($$$3 \le n \le 10^5$$$) — the length of the array.

The second line contains $$$n$$$ integers $$$a_1, a_2, \ldots, a_n$$$ ($$$0 \le a_i \le 1$$$) — the elements of the array.

Output

Print "YES" (without quotes) if the answer exists, otherwise print "NO" (without quotes). You can print each letter in any case (upper or lower).

If there is an answer, in the second line print an integer $$$m$$$ ($$$0 \le m \le (\lfloor \frac{n}{3} \rfloor + 12)$$$) — the number of operations in your answer.

After that in ($$$i + 2$$$)-th line print the $$$i$$$-th operations — the integers $$$x_i, y_i, z_i$$$. You can print them in arbitrary order.

Examples

Input

5

1 1 0 1 1

Output

YES

2

1 3 5

2 3 4

Input

3

0 1 0

Output

NO

Note

In the first sample the shown output corresponds to the following solution:

- 1 1 0 1 1 (initial state);
- 0 1 1 1 0 (the flipped positions are the first, the third and the fifth elements);
- 0 0 0 0 0 (the flipped positions are the second, the third and the fourth elements).

Other answers are also possible. In this test the number of operations should not exceed $$$\lfloor \frac{5}{3} \rfloor + 12 = 1 + 12 = 13$$$.

In the second sample the only available operation is to flip all the elements. This way it is only possible to obtain the arrays 0 1 0 and 1 0 1, but it is impossible to make all elements equal to zero.

Codeforces (c) Copyright 2010-2018 Mike Mirzayanov

The only programming contests Web 2.0 platform

Server time: Dec/12/2018 02:47:34 (f2).

Desktop version, switch to mobile version.

Supported by

User lists

Name |
---|