program sss;
var f,g:text;
    n,i,u,p,s,k:longint;
    a,c:array[1..5000005] of longint;
begin
assign(f,'deque.in'); reset(f);
assign(g,'deque.out'); rewrite(g);
readln(f,n,k);
  for i:=1 to n do
    readln(f,a[i]);
    p:=1;
    u:=0;
    s:=0;
      for i:=1 to n do
        begin
          while (p<=u) and (a[i]<=a[c[u]]) do
            u:=u-1;
            u:=u+1;
            c[u]:=i;
            if i>=k then
            begin
            if c[p]=i-k then
              p:=p+1;
              s:=s+a[c[p]];
            end;
        end;
      write(g,s);
close(f);
close(g);
end.