/*
AizuOnline A2018
Princess's Gamble
*/
#include <stdio.h>
#include <float.h>

int M,N,P;
int hyousuu[100];
long int sousuu;
long int haitou;

main()
{
  int i;

  while(EOF!=scanf("%d %d %d",&N,&M,&P) && (N || M || P))
    {
      sousuu=0;
      for(i=0;i<N;i++)
	{
	  scanf("%d",&hyousuu[i]);
	  sousuu += hyousuu[i];
	}
      haitou = (double)sousuu / (double)hyousuu[M-1] * (double)P;

      printf("%ld\n",haitou);
    }
return(0);
}