# #2632. 「BalticOI 2011 Day1」打开灯泡 Switch the Lamp On

#### 题目描述

$N\times M$ 个这样的元件，你想将其排列成 $N$$M$ 列放在电路板上。电路板的左上角连接电源，右下角连接灯泡。

Casper is designing an electronic circuit on a $N ×M$ rectangular grid plate. There are $N ×M$ square tiles that are aligned to the grid on the plate. Two (out of four) opposite corners of each tile are connected by a wire.
A power source is connected to the top left corner of the plate. A lamp is connected to the bottom right corner of the plate. The lamp is on only if there is a path of wires connecting power source to lamp. In order to switch the lamp on, any number of tiles can be turned by $90°$ (in both directions).
In the picture above the lamp is off. If any one of the tiles in the second column from the right is turned by $90°$ , power source and lamp get connected, and the lamp is on.
Write a program to find out the minimal number of tiles that have to be turned by $90°$ to switch the lamp on.

#### 输入格式

The first line of input contains two integer numbers $N$ and $M$, the dimensions of the plate. In each of the following $N$ lines there are $M$ symbols – either \ or / – which indicate the direction of the wire connecting the opposite vertices of the corresponding tile.

#### 输出格式

There must be exactly one line of output. If it is possible to switch the lamp on, this line must contain only one integer number: the minimal number of tiles that have to be turned to switch on the lamp. If it is not possible, output the string: NO SOLUTION

3 5
\\/\\
\\///
/\\\\

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