#include <fstream.h>
#include <stdio.h>

double a[30],p;
int nr,n,kk;

void bk(int ant, int k, double s){
     
     if (k==kk+1){p+=s;++nr;}
     else for (int i=ant+1;i<n-(kk-k)+1;i++) bk(i,k+1,s*a[i]);
}
     


int main()
{int i;
 ifstream f("dezastru.in");
 freopen ("dezastru.out", "w",stdout);
 f>>n>>kk;
 for (i=1;i<=n;i++) f>>a[i];
 bk(0,1,1);
 printf("%lf\n",p);
 p/=nr;
 printf("%lf",p);
 f.close();
 return 0;
}