let e18 =
    let input = System.IO.File.ReadAllLines(@"C:\Users\Peter\source\repos\ProjectEuler\ProjectEuler\pyramid.txt")
    let parsed =
        input
        |> Array.map (fun str ->
            str.Split([|' '|])
            |> Array.map int
            |> List.ofArray)
        |> List.ofArray
        |> List.rev
    let rec getMaxSum (pyramid: int list list) =
        match pyramid with
        | l when List.length l = 1 -> l.Head.Head
        | baseOfPyramid::secondLayer::rest ->
            let possiblePairs = (List.windowed 2 baseOfPyramid)
            getMaxSum
                (List.append
                [((List.map2
                    (fun block pair -> block + (List.max pair))
                    secondLayer
                    possiblePairs))]
                rest)
        | _ -> 0

    getMaxSum parsed