13.若mmm,nnn满足m2−3m−1=0m^{2}-3m-1=0m2−3m−1=0,n2−3n−1=0n^{2}-3n-1=0n2−3n−1=0,且m≠nm\ne nm=n,则nm+mn\frac{n}{m}+\frac{m}{n}mn+nm的值为((( )))