5-4+3-2*1=2
5-(4-3)-2*1=2
5-(4-3)*2-1=2
(5+4)/3-2+1=2
(5-4)*3-2+1=2
(5-4)+(3-2)*1=2 等
(9*9-9)/9+9=17
(9+9)/9+9+9=20