program p1;
var a,d:array[0..50000005] of  longint;
    f,g:Text;
    i,n,j,k,u,p:longint;
    s:int64;
    b1,b2:array[0.. 1 shl 23] of char;
begin
assign(f,'deque.in');reset(F);
assign(g,'deque.out');rewrite(G);
settextbuf(f,b1);
settextbuf(g,b2);
readln(f,n,k);
for i:=1 to n do readln(f,a[i]);
p:=1;
u:=0;
for i:=1 to n do begin
         while (p<=u) and (a[i]<=a[d[u]])  do dec(U);
         inc(u);
         d[u]:=i;
          if i>=k then s:=s+a[d[p]];
          if d[p]=i-k+1 then inc(P);
         end;
writeln(g,s);
close(F);
close(G);
end.