program alex;
var f:text;
    i,n,k,j,ls,li:longint;
    s:int64;
    a,c:array[1..5000000]of longint;
begin
assign(f,'deque.in');reset(f);
readln(f,n,k);
for i:=1 to n do
    read(f,a[i]);
close(f);
li:=1;
ls:=0;
s:=0;
for i:=1 to n do
    begin
    while(li<=ls)and(a[i]<=a[c[ls]])do
          ls:=ls-1;
    ls:=ls+1;
    c[ls]:=i;
    if c[li]=i-k then li:=li+1;
    if i>=k then s:=s+a[c[li]];
    end;
assign(f,'deque.out');rewrite(f);
write(f,s);
close(f);
end.