{
TASK: seq
LANG: Pascal
}
program seq;

var a          : integer;
    n, i       : longword;
    sum        : int64;
    k          : byte;
    chis, znam : longword;

begin
readln(n,k);

sum := 0; chis := 1; znam := 1;


for i := 1 to n do
 begin
  read(a);
  sum := sum + a;
 end;


for i := 1 to k do
 chis := chis*(n-k-1+i);
 if chis mod i = 0
  then chis := chis div i
  else znam := znam*i;

chis := chis div znam;

writeln(chis*sum);
end.