var     f,g:text;
        bufin,bufout:array[1..65000]of byte;
        ind,c:array[-1..5000010] of longint;
        i,n,k:longint;
        l,pr,sum,x:int64;
begin
        assign(f,'deque.in');
        assign(g,'deque.out');
        reset(f);
        rewrite(g);
        settextbuf(f,bufin);
        settextbuf(g,bufout);
        readln(f,n,k);
        pr:=1;
        l:=0;
        for i:=1 to k do begin
                read(f,x);
                inc(l);
                while (x<c[l-1]) and (l>1) do dec(l);
                c[l]:=x;
                ind[l]:=i;
        end;
        sum:=c[1];
        for i:=k+1 to n do begin
                read(f,x);
                if ind[pr]=i-k then inc(pr);
                inc(l);
                while (x<c[l-1]) and (l>pr) do dec(l);
                c[l]:=x;
                ind[l]:=i;
                sum:=sum+c[pr];
        end;
        writeln(g,sum);
        close(g);
end.