/*
 * @(#) smt1_7.c - Program for calculation of the hitting factor of
 * some bombs, variant 3 (Task 1_7 at the Special Military Training course).
 * (c) 1996 Ivan Maidanski <ivmai@chat.ru> http://ivmai.chat.ru
 * Freeware program source. All rights reserved.
 **
 * Language: ANSI C
 * Tested with: Borland C++ v3.1
 * Last modified: 1996-12-06 18:00:00 GMT+03:00
 */

#include <stdio.h>

float p[100];

int main()
{
 int m,k,i,j,cnt,test;
 float s,w;
 printf("Input M:\n");
 scanf("%d",&m);
 printf("Input K:\n");
 scanf("%d",&k);
 for (i=0;i<m;i++)
 {
  printf("Input R(%d):\n",i+1);
  scanf("%f",&p[i]);
 }
 w=0.0;
 for (j=(1<<m)-1;j>=0;j--)
 {
  s=1.0;
  cnt=0;
  test=j;
  for (i=0;i<m;i++)
   s*=(test & 1) ? (cnt++,p[i]) : (1.0-p[i]) , (test>>=1);
  if (cnt==k)
   w+=s;
 }
 printf("\n W=%f\n\n",w);
 return 0;
}