Shelter

Example

Input

4 1 0 0 3 0 3 3 0 3 1 1

Output

2.0000000000

inputFormat

Input

4 1 0 0 3 0 3 3 0 3 1 1

outputFormat

Output

2.0000000000

样例

4 1
0 0
3 0
3 3
0 3
1 1

2.0000000000