CF837B.Flag of Berland

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题目描述

The flag of Berland is such rectangular field $n×m$ that satisfies following conditions:

Flag consists of three colors which correspond to letters 'R', 'G' and 'B'.
Flag consists of three equal in width and height stripes, parralel to each other and to sides of the flag. Each stripe has exactly one color.
Each color should be used in exactly one stripe.

You are given a field $n×m$ , consisting of characters 'R', 'G' and 'B'. Output "YES" (without quotes) if this field corresponds to correct flag of Berland. Otherwise, print "NO" (without quotes).

输入格式

The first line contains two integer numbers $n$ and $m$ ( $1<=n,m<=100$ ) — the sizes of the field.

Each of the following $n$ lines consisting of $m$ characters 'R', 'G' and 'B' — the description of the field.

输出格式

Print "YES" (without quotes) if the given field corresponds to correct flag of Berland . Otherwise, print "NO" (without quotes).

输入输出样例

输入#1

6 5
RRRRR
RRRRR
BBBBB
BBBBB
GGGGG
GGGGG

输出#1

YES

输入#2
```
4 3
BRG
BRG
BRG
BRG
```
输出#2
```
YES
```

输入#3

6 7
RRRGGGG
RRRGGGG
RRRGGGG
RRRBBBB
RRRBBBB
RRRBBBB

输出#3

NO

输入#4
```
4 4
RRRR
RRRR
BBBB
GGGG
```
输出#4
```
NO
```

说明/提示

The field in the third example doesn't have three parralel stripes.

Rows of the field in the fourth example are parralel to each other and to borders. But they have different heights — 2, 1 and 1.

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