a1x1+a2x2+a3x3+a4x4a7x1+a6x2+a5x3+a8x4a11x1+a12x2+a13x3+a10x4a17x1+a16x2+a15x3+a14x4=1432=2341=3412=4321
Suppose a1,a2,a3,…,a15,a16,a17 form an arithmetic progression such that a9=257 . Find the value of ⌊x1+x2+x3+x4⌋.