题目描述

输入格式

输出格式

Output a single integer, the minimum number of leaking components that could give rise to the observed leak test results. If no set of leaking components could give rise to the observed results, instead output the single word impossible.

样例

4 
1 -1 P 
2 2 P 
-1 3 N 
-2 -1 -

1

2 
0 0 N 
1 2 P

impossible

提示

by Shore