var n,i,k,min,j,pos:longint;
    s:int64;
    v:array[1..5000000] of longint;
begin
assign(input,'deque.in');
reset(input);
read(input,n,k);
min:=maxlongint;
for i:=1 to k do begin
    read(input,v[i]);
    if min>=v[i] then begin
       min:=v[i];
       pos:=i;
       end;
    end;
s:=min;
for i:=k+1 to n do begin
    read(input,v[i]);
    if v[i]<=min then begin
       min:=v[i];
       pos:=i;
       end;
    if pos<=i-k then begin
       min:=maxlongint;
       for j:=i downto i-k+1 do
           if v[j]<min then begin
              min:=v[j];
              pos:=j;
              end;
       end;
    s:=s+min;
    end;
close(input);
assign(output,'deque.out');
rewrite(output);
write(output,s);
close(output);
end.