#include <stdio.h>

#define MAX  10240

int len[MAX], n, k;

int howmany (int cm)
{
    int cnt = 0, i;
    for ( i = 0;  i < n;  ++i )
	cnt += (len[i] / cm);
    return cnt;
}

void readcm (int *p)
{
    int a, b;
    scanf ("%d.%d", &a, &b);
    *p = a * 100 + b;
}

int main (void)
{
    int i, max, min;
    for ( ; ; )
    {
	scanf ("%d%d", &n, &k);
	if ( !n || !k )  break;
	max = 0;
	for ( i = 0;  i < n;  ++i )
	{
	    readcm (len + i);
	    if ( len[i] > max )  max = len[i];
	}

	++max;
	min = 0;
	while ( min+1 < max )
	    if ( howmany ((min+max)/2) < k )
		max = (min+max)/2;
    	    else
		min = (min+max)/2;
	printf ("%d.%02d\n", min/100, min%100);
    }
    return 0;
}