var     i,j,n,k,min:longint;
        s:int64;
        f1,f2:text;
        a:array[1..5000000] of longint;

begin
  assign(f1,'deque.in');
  reset(f1);
  assign(f2,'deque.out');
  rewrite(f2);
  readln(f1,n,k);

  for i:=1 to n do
    readln(f1,a[i]);

  s:=0;
  for i:=1 to n-k+1 do
    begin
      min:=10000000;
      for j:=i to i+k-1 do
        if a[j]<min then min:=a[j];
      s:=s+min;
    end;

  writeln(f2,s);
  close(f2);
end.