side of the suitcase will be smallest if they arranged in 2 x 2 way so find all possible sides of that arrangement
$ side1 = $ a [ 0 ] + $ a [ 3 ] ; $ side2 = $ a [ 1 ] + $ a [ 2 ] ; $ side3 = $ a [ 0 ] + $ a [ 1 ] ; $ side4 = $ a [ 2 ] + $ a [ 3 ] ;