/* 
TASK:seq
LANG:C++
*/

#include <stdio.h>
long long coef[32] = {0},prod = 0,sum = 0;
int j;
int main()
{
    int n,k,a,i;
    scanf("%d %d",&n,&k);
    coef[0] = 1;
    for(i = 0;i < n;i++)
    {
          scanf("%d",&a);
          sum += a;
          for(j = k;j >= 0;j--)
          {
                coef[j] = coef[j] + coef[j-1];
          }
          if(i == n - 2)
          {
               prod = coef[k];
          }
    }
    printf("%lld\n",sum*prod);
    //Vsqko 4ilso u4astva v redicata C(n,k) na broi pyti
    //nqma razlika na 4islata sledovatelno u4astvat ekvivaletno
    return 0;
}
 
