输入：第一行是3个正整数，m(1≤m≤100)，n(1≤n≤100)，D(1≤D≤100)。表示原野是m*n的矩阵，法里奥最多只能飞行距离为D。

接下来的m行每行有n个字符，相互之间没有空格。P表示当前位置是平地，L则表示湖泊。假定(1,1)和(m,n)一定是平地。

输出：一个整数，表示法里奥到达基地需要的最短时间。如果无法到达基地，则输出impossible。-Input: The first line is the three positive integers, m (1 ≤ m ≤ 100), n (1 ≤ n ≤ 100), D (1 ≤ D ≤ 100). That wilderness is m* n matrix, Fario maximum flight distance of D. The next m lines with n characters per line, with no spaces between each other. P indicates the current position is flat, L indicates the lake. Assume that (1,1) and (m, n) must be flat. Output: An integer representation of Leo the minimum time required to reach base. If you can not reach the base, then the output impossible.