x=[0];
N=2100;
for last=2:(N+1)
    forbidden=[];
    for first=1:(last-2)
        xfirst=x(first);
        nforbidden=floor((last-first)/2);
        forbidden=[forbidden,x((first+1):(first+nforbidden))+x((last-1):-1:(last-nforbidden))-xfirst];
    end
    forbidden=unique(forbidden(forbidden>=0));
    xlast=0;
    forbiddenindex=1;
    while forbiddenindex<=length(forbidden) & xlast==forbidden(forbiddenindex)
        xlast=xlast+1;
        forbiddenindex=forbiddenindex+1;
    end
    x(last)=xlast;
end