open System
open System.Collections.Generic

module InputUtility =
    let InputTokens = new Queue<string>()

    let EnsureInput () =
        if InputTokens.Count = 0 then
            let input = Console.ReadLine ()
            let s = input.Split ([|' '|], StringSplitOptions.RemoveEmptyEntries)
            if s.Length > 0 then
                for x in s do InputTokens.Enqueue(x)
                true
            else false
        else true

    let rec ReadNext () =
        if EnsureInput () then InputTokens.Dequeue ()
        else ReadNext ()

    let ReadNextInt () = ReadNext () |> int

    let Read2Int () = ReadNextInt (), ReadNextInt ()

    let Read3Int () = ReadNextInt (), ReadNextInt (), ReadNextInt ()

    let ReadListOf f n =
        let rec loop acc = function
            | 0 -> List.rev acc
            | c -> loop ((ReadNext () |> f) :: acc) (c-1)
        loop [] n

    let MultipleCaseWithId f =
        let caseNum = ReadNextInt ()
        let rec loop index =
            if index = caseNum then ()
            else
                f index
                loop (index + 1)
        loop 0

    let MultipleCase f = MultipleCaseWithId (fun _ -> f ())

    let ReadList n =
        let rec loop acc = function
            | 0 -> List.rev acc
            | c -> loop (ReadNext () :: acc) (c-1)
        loop [] n

open InputUtility

module ARC076 =
    let private Mod = 1000000007L

    let private Reconciled () =
        let rec g x r =
            if x = 0 then r
            else g (x - 1) (r * int64 x % Mod)
        let f x = g x 1L
        let n, m =
            let a, b = Read2Int ()
            if a > b then b, a else a, b
        if n + 1 < m then 0L
        elif n + 1 = m then
            f m * f n % Mod
        else
            2L * f n * f n % Mod
        |> printfn "%d"

    let Entry = Reconciled

ARC076.Entry ()