function s = reduce(p);
s = cell(length(p),1);
for i = 1:length(p)
    s{i} = i;
end
while size(s) > 2
    [p,i] = sort(p);
    p(2) = p(1) + p(2);
    p(1) = [];
    s = s(i);
    s{2} = {s{1},s{2}};
    s(1) = [];
end