13. In the expression $9+8-7 \times 6 \div 5+4-3 \times 2 \div 1$, add parentheses arbitrarily so that the calculation result $\mathrm{N}$ is a natural number. The minimum value of $\mathrm{N}$ is
【Analysis】 $[9+(8-7) \times 6] \div 5+4-3 \times 2 \div 1=1$