var v,c:array[1..5000010] of longint;
    s,d,i,n,k:longint;
    sum:int64;
    f:text;
begin
assign(f,'deque.in');reset(f);
assign(output,'deque.out'); rewrite(output);
readln(f,n,k);
s:=1; d:=0;
for i:=1 to n do
  begin
    readln(f,v[i]);
    while (s<=d)and(v[i]<=v[c[d]]) do dec(d);
    inc(d);
    c[d]:=i;
    if c[s]=i-k then inc(s);
    if i>=k then sum:=sum+v[c[s]];
  end;
writeln(sum);
close(output);
close(f);
end.