A Problem about Polyline

578A1700· expert1s256 MB⌨ stdin/stdout

#geometry #math

Examples

Sample 1of 3

Input

3 1

Output

1.000000000000

Sample 2of 3

Input

1 3

Output

-1

Sample 3of 3

Input

4 1

Output

1.250000000000

578A.cpp

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Ln 11·137 BGNU C++20 (64)