Consider an $n \times n$ grid whose squares may have traps. It is not allowed to move to a square with a trap.
Your task is to calculate the number of paths from the upper-left square to the lower-right square. You can only move right or down.
The first input line has an integer $n$ : the size of the grid.
After this, there are $n$ lines that describe the grid. Each line has $n$ characters: . denotes an empty cell, and * denotes a trap.
Print the number of paths modulo $10^9+7$ .