Treasures in a map (2) P60796

Write a program that, given a map with treasures and obstacles, computes the distance from a given initial position to the nearest accessible treasure. The allowed movements are horizontal or vertical, but not diagonal.

Input

Input begins with the number of rows $n > 0$ and the number of columns $m > 0$ of the map. Follow $n$ rows with $m$ characters each. A dot indicates an empty position, an ‘X’ indicates an obstacle, and a ‘t’ indicates a treasure. Finally, two numbers $r$ and $c$ indicate the initial row and column (both of them starting at 1) where we must start looking for treasures. You can assume that $r$ is between 1 and $n$, that $c$ is between 1 and $m$, and that the initial position is always empty.

Output

Print the minimum number of steps to reach a treasure strating from the initial position. If no treasure is accessible, tell so.