CF475C.Kamal-ol-molk's Painting

The first line of input contains two integers $n$ and $m$ , ( $1<=n,m<=1000$ ), denoting the height and width of the painting.

The next $n$ lines contain the painting. Each line has $m$ characters. Character 'X' denotes an altered cell, otherwise it's showed by '.'. There will be at least one altered cell in the painting.

Print the minimum area of the brush in a line, if the painting is possibly altered, otherwise print $-1$ .

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