ll@n,m=4n*n,@k,b=0;rep(m){char@c;b+=c&1;}ll@c[m],e[];rep(y,2n)rep(x,n)e[n*y+x]=c[2n*y+x]+c[~x-2n*~y];rsortA(m,c);rsortA(m/2,e);wt(max(sum(c(b)),b&1?0:sum(e(b/2))+k));