var n,k,x,i,first,last:longint;
a,deque:array[0..5000000] of longint;
s:int64;


begin
assign(input,'deque.in');
assign(output,'deque.out');
reset(input);
rewrite(output);
read(n,k);

for i:=1 to n do
       read(a[i]);


first:=1;
last:=0; s:=0;

for i:=1 to n do
        begin
        while (a[i]<a[deque[last]]) and (last>0) do dec(last);
        inc(last);
        deque[last]:=i;
        if (deque[first]=i-k) then
                        inc(first);
        if i>=k then inc(s,a[deque[first]]);
        end;
write(s);
close(input);
close(output);
end.