-- True-False DP (bitset) local mfl, mce = math.floor, math.ceil local bls, brs = bit.lshift, bit.rshift local bor, band = bit.bor, bit.band local bxor = bit.bxor local TFDP = {} TFDP.initialize = function(self, lim) self.lim = lim self.sz = 30 self.way = true self.bcnt = mce((lim + 1) / self.sz) self.b1, self.b2 = {1}, {} for i = 2, self.bcnt do self.b1[i] = 0 end self.curmax = 0 end TFDP.add = function(self, v) local src = self.way and self.b1 or self.b2 local dst = self.way and self.b2 or self.b1 self.way = not self.way local bcnt = self.bcnt for i = 1, bcnt do dst[i] = src[i] end local sz = self.sz local jump, rem = mfl(v / sz), v % sz for i = 1, bcnt - jump do local v1 = src[i] % bls(1, sz - rem) dst[i + jump] = bxor(dst[i + jump], v1 * bls(1, rem)) end for i = 1, bcnt - jump - 1 do local v2 = brs(src[i], sz - rem) dst[i + jump + 1] = bxor(dst[i + jump + 1], v2) end end TFDP.query = function(self, x) local group = mfl(x / self.sz) + 1 local idx = x - (group - 1) * self.sz local tbl = self.way and self.b1 or self.b2 return band(tbl[group], bls(1, idx)) ~= 0 end local tf = TFDP local n = io.read("*n") local lim = n * 2000 tf:initialize(lim) for i = 1, n do local a = io.read("*n") tf:add(a) end local ret = 0 for i = 1, lim do if tf:query(i) then ret = bxor(ret, i) end end print(ret)