### Machine Surfaces

Time Limit: 1000 ms Memory Limit: 65536 KiB

#### Problem Description

An imaging device furnishes digital images of two mechined surfaces that eventually will be assembled in contact with each other. The roughness of this final contact is to be estimated.

A digital image is composed of the two characters, "X" and " " (space). There are always 25 columns to an image, but the number of rows, N, is variable. Column one (1) will always have an "X" in in and will be part of the surface. The left surface can extend to the right from column (1) as contiguous X's.

Similarly, column 25 will always have an "X" in it and will be part of the right surface. The right surface can extend to the left from column 25 as contiguous X's.

Digital-Image View of Surfaces:

XXXX                     XXXXX
XXX                    XXXXXXX
XXXXX                     XXXX
XX                      XXXXXX
.                            .
.                            .
.                            .
XXXX                      XXXX
XXX                     XXXXXX


In each row of the image, there can be zero or more space characters separating the left surface from the right surface. There will never be more than a single blank region in any row.

Fro each image given, you are to determine the total "void" that will exist after the left surface has been brought into contact with the right surface. The "void" is the total count of the spaces that remains between the left and right surfaces after they have been brought into contact.

The two surfaces are brought into contact by displacing them strictly horizontally towards each other until a rightmost "X" of the left surface of some row is immediately to the left of the leftmost "X" of the right surface of that row. There is no rotation or twisting of there two surfaces as thay are brought into contact; they reamin rigid, and only move horizontally.

Note: The original image may show the two surfaces already in contact, in which case no displacement enters into the contact roughness estimation.

#### Input

The input consists of a series of digital images. Each imaga data set has the following format:

First line - A single unsigned integer, N, with value greater than zero (0) and less than 13. The first digit of N will be the first character on a line.

Next N lines - Each line has exactly 25 characters; one or more X's, then zero or more spaces, then one or more X's.

The end of data is signaled by a null data set having a zero on the first line of an image set and no furher data.

#### Output

In the example input file below, the spaces have been replaced with the character "B" for ease of reading. The actual input file will use the ASCII-space character, not "B".

#### Sample Input

4
XXXXBBBBBBBBBBBBBBBBXXXXX
XXXBBBBBBBBBBBBBBBXXXXXXX
XXXXXBBBBBBBBBBBBBBBBXXXX
XXBBBBBBBBBBBBBBBBBXXXXXX
2
XXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXX
1
XXXXXXXXXXBBBBBBBBBBBBBXX
0

#### Sample Output

4
0
0