{$MODE OBJFPC}
uses math; 
const
    nmax = trunc(1e4) + 10;
    oo = trunc(1e18);
var
    n,k,i : integer;
    c : array[1..nmax] of integer;
    cp,res : int64;
procedure turn (n,i : integer);
var
    j : integer;
    l,r : integer;
begin
    cp:= cp + c[i];
    l:= i - k;
    if l > 0 then
        for j:=1 to l-1 do
            turn(l,j);
    r:= i + k;
    if r < n-1 then
        for j:=r+1 to n-1 do
            turn(n-r,j);
end;
BEGIN
    readln(n,k);
    for i:=1 to n do
        read(c[i]);
    res:= oo;
    for i:=0 to n do
        begin
            cp:= 0;
            turn(n,i);
            res:= min(cp,res);
        end;
    write(res);
END.