local ior = io.input()
local n = ior:read("*n")
local v = ior:read("*n")
local ta, tb = {}, {}
ta[1] = v
tb[1] = 0
local mma = math.max
for i = 2, n do
  v = ior:read("*n")
  ta[i] = mma(ta[i - 1], tb[i - 1] + v)
  tb[i] = mma(tb[i - 1], ta[i - 1])
end
print(mma(ta[n], tb[n]))