open System.Text.RegularExpressions
open System

let input = "378282246310005"

let digits = input |> Seq.filter System.Char.IsNumber |> Seq.map (string >> int)
if (digits |> Seq.length) <> 0 then
    let multiply i n = 
        match i % 2 with 
        | 1 when n < 5 -> n * 2 
        | 1 -> (n * 2) - 9 
        | _ -> n
    let sum = digits |> Seq.rev |> Seq.mapi multiply |> Seq.sum
    sum % 10 = 0   
else
    false