Program deque;
 var a:array [1..5000000] of longint;
     i,n,k,min,posmin,j,min2,posmin2:longint;
     b1:array [1..1 shl 16] of char;
     s:int64;
     fi,fo:text;
begin
assign(fi,'deque.in');
 assign(fo,'deque.out');
settextbuf(fi,b1);
reset(fi);
 rewrite(fo);
readln(fi,n,k);
for i:=1 to n do readln(fi,a[i]);
min:=a[1];
for i:=2 to k do
 if a[i]<=min then begin
                   min:=a[i];
                   posmin:=i;
                   end;
 s:=s+min;
 min2:=a[posmin+1];
 posmin2:=posmin+1;
for i:=k+1 to n do begin
   if a[i]<=min then begin
                      min:=a[i];
                      posmin:=i;
                      min2:=a[i+1];
                      posmin2:=i+1;
                      end;
 if a[i]<=min2 then begin
                        min2:=a[i];
                        posmin2:=i;
                        end;
  if posmin<i-k+1 then begin
                        min:=min2;
                        posmin:=posmin2;
                        min2:=a[i+1];
                        posmin2:=i+1;
                        end;
 s:=s+min;
 end;
writeln(fo,s);
close(fo);
end.
    if