open System

let valid target window =

let pairs = seq { for x in window do for y in window do if x <> y && x + y = target then yield (x, y) } in

(Seq.length pairs) <> 0

let part1 input =

let rec loop all =

let window = all |> Seq.truncate 25 |> Seq.cache in

let next = all |> Seq.item 25 in

if not (valid next window) then next else loop (Seq.tail all)

in

loop input

let part2 input part1answer =

let a = input in

let N = Seq.length a in

seq {

for n = 2 to N do

for i = 0 to (N - 1 - n) do

let s = a |> Seq.skip i |> Seq.take n

if (Seq.sum s) = part1answer then

yield (Seq.min s) + (Seq.max s)

} |> Seq.head

let private main (args:string[]) : int =

let filename = args.[0] in

let input = seq { for line in IO.File.ReadAllLines filename do yield int64 line } |> Seq.cache in

let part1answer = part1 input in

printfn "%d" part1answer

let part2answer = part2 input part1answer in

printfn "%d" part2answer

0

#if INTERACTIVE

fsi.CommandLineArgs |> Array.toList |> List.tail |> List.toArray |> main

let entryPoint args = main args