program deque;
var d,v:array[-1..5000001] of longint;
    n,k,i,p,u:longint;
    f,g:text;
    s:int64;
begin
assign(f,'deque.in');
assign(g,'deque.out');
reset(f);
rewrite(g);
read(f,n,k);
{for i:=1 to n do
    readln(f,v[i]); }
p:=1;
u:=0;
s:=0;
for i:=1 to k do
    begin
    readln(f,v[i]);
    while (p<=u) and (v[i]<=v[d[u]]) do dec(u);
    inc(u);
    d[u]:=i;
    end;
s:=s+v[d[p]];
for i:=k+1 to n do
    begin
    readln(f,v[i]);
    if i-d[p]=k then inc(p);
    while (p<=u) and (v[i]<=v[d[u]]) do dec(u);
    inc(u);
    d[u]:=i;
    s:=s+v[d[p]];
    end;
close(f);
writeln(g,s);
close(g);
end.