maximum shortest distance

There are n points in the plane. Your task is to pick k points (k>=2), and make the closest points in these k points as far as possible.

For each case, the first line contains two integers n and k. The following n lines represent n points. Each contains two integers x and y. 2<=n<=50, 2<=k<=n, 0<=x,y<10000.

For each case, output a line contains a real number with precision up to two decimal places.

3 2
0 0
10 0
0 20

22.36

alpc50

2010 ACM-ICPC Multi-University Training Contest（15）——Host by NUDT