{-# OPTIONS_GHC -O2 -funbox-strict-fields #-}
{-# OPTIONS_GHC -fno-warn-unused-imports #-}
{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
{-# OPTIONS_GHC -fno-warn-unused-binds #-}
{-# OPTIONS_GHC -fno-warn-incomplete-patterns #-}
{-# OPTIONS_GHC -fno-warn-name-shadowing #-}
{-# LANGUAGE OverloadedStrings #-}
-- {-# LANGUAGE FlexibleContexts #-}
-- {-# LANGUAGE MultiWayIf #-}
-- {-# LANGUAGE BangPatterns #-}
-- {-# LANGUAGE ViewPatterns #-}
-- {-# LANGUAGE TupleSections #-}

import           System.IO hiding (char8)
import           Control.Applicative
import           Control.Monad
import           Data.List
import           Data.Tuple
import           Data.Int
import           Data.Char
import           Data.Function (on)
import           Data.Ord (comparing)
import           Data.Monoid (mappend)
import           Data.Array
-- import           Data.Array.Unboxed
-- import           Data.Array.IArray
-- import           Data.Array.ST
-- import           Data.Array.MArray
-- import           Data.Array.Unsafe
-- import           Data.Array.Base(unsafeRead, unsafeWrite)
-- import           Data.Array.IO
import           Data.Ix
import           Data.Maybe
-- import           Data.Monoid hiding ((<>))
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy.Char8 as BL
import           Data.ByteString.Builder
-- import           Data.Graph
-- import           Data.Vector.Unboxed ((//), (++), (!), (!?))
-- import qualified Data.Vector.Unboxed as U
-- import           Data.IntSet (IntSet)
-- import qualified Data.IntSet as IntSet
-- import           Data.IntMap.Strict (IntMap)
-- import qualified Data.IntMap.Strict as IntMap
-- import           Data.Sequence ((|>), (<|), (><),ViewR(..), ViewL(..), Seq)
-- import qualified Data.Sequence              as Seq
-- import           Data.Foldable (toList, minimumBy)
-- import           Debug.Trace

main = do
  (n, m) <- readInt642 <$> BS.getLine
  print $ solve n m

solve n m
  | abs (n - m) == 0 = 2 *% solve' n m
  | abs (n - m) == 1 = solve' n m
  | otherwise        = 0

solve' n m = fact n *% fact m

fact 0 = 1
fact n = fact (n-1) *% n

-- fact 0 = 1
-- fact n = m' *% m' * bino n m *% if even n then 1 else m+1
--   where
--     m = n`div`2
--     m' = fact m
--
-- bino n k = bino' n (if k*%2 <= n then k else n-k) where
--   bino' _ 0 = 1
--   bino' 0 _ = 0
--   bino' n k = bino (n-1) (k-1) *% n `div` k

-- mod modules --

modNum = 1000000007::Int64

modd a = a `mod` modNum

(+%) a b = modd (modd a + modd b)
infixl 6 +%

(-%) a b = modd (modd a - modd b + modNum)
infixl 6 -%

-- usable on Int64
(*%) a b = modd (modd a * modd b)
infixl 7 *%

-- usable only if modNum is prime
(/%) a b = a *% powerMod b (modNum-2) modNum where
  -- SICP Power iteration
  power :: Integral a => (t -> t -> t) -> t -> a -> t -> t
  power _ _ 0 e = e
  power f a n e = power f (f a a) (div n 2) (if odd n then f a e else e)
  powerMod a n _ = power (*%) a n 1
infixl 7 /%

--  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --  --

getInt1 :: IO Int
getInt1 = readInt1 <$> BS.getLine

getInt2 :: IO (Int, Int)
getInt2 = readInt2 <$> BS.getLine

getInt3 :: IO (Int, Int, Int)
getInt3 = readInt3 <$> BS.getLine

getInts :: IO [Int]
getInts = readInts <$> BS.getLine

getIntN :: Int -> IO [Int]
getIntN n = map readInt1 <$> replicateM n BS.getLine

format :: Show a => Maybe a -> IO ()
format Nothing = putStrLn "NO"
format (Just a) = putStrLn "YES" >> print a

-- [1,2,3] -> 1 2 3
putInts :: [Int] -> IO ()
-- putInts [] = return ()
-- putInts xs = BL.putStrLn . toLazyByteString . foldl1 mappend . intersperse (char8 ' ') $ map intDec xs
putInts = putStrLn . unwords . map show

readInt1 :: BS.ByteString -> Int
readInt1 = fst . fromJust . BS.readInt

readInt2 :: BS.ByteString -> (Int,Int)
readInt2 = toTuple . readInts

readInt3 :: BS.ByteString -> (Int,Int,Int)
readInt3 = toTriple . readInts

readInts :: BS.ByteString -> [Int]
readInts =  map readInt1 . BS.words

readInt641 :: BS.ByteString -> Int64
readInt641 = fromIntegral . fst . fromJust . BS.readInteger

readInt642 :: BS.ByteString -> (Int64,Int64)
readInt642 = toTuple . readInt64s

readInt643 :: BS.ByteString -> (Int64,Int64,Int64)
readInt643 = toTriple . readInt64s

readInt64s :: BS.ByteString -> [Int64]
readInt64s =  map readInt641 . BS.words

readInteger1 :: BS.ByteString -> Integer
readInteger1 = fst . fromJust . BS.readInteger

readInteger2 :: BS.ByteString -> (Integer,Integer)
readInteger2 = toTuple . readIntegers

readInteger3 :: BS.ByteString -> (Integer,Integer,Integer)
readInteger3 = toTriple . readIntegers

readIntegers :: BS.ByteString -> [Integer]
readIntegers =  map readInteger1 . BS.words

toTuple :: [a] -> (a, a)
toTuple [x, y] = (x, y)

toTriple :: [a] -> (a, a, a)
toTriple [x, y, z] =(x, y, z)

fromTuple :: (a, a) -> [a]
fromTuple (x, y) = [x, y]

fromTriple :: (a, a, a) -> [a]
fromTriple (x, y, z) = [x, y, z]

-- if not applying, use "id"

applyTuple :: (a -> a') -> (b -> b') -> (a, b) -> (a', b')
applyTuple f g (x, y) = (f x, g y)

applyTriple :: (a -> a') -> (b -> b') -> (c -> c') -> (a, b, c) -> (a', b', c')
applyTriple f g h (x, y, z) = (f x, g y, h z)

-- @since 4.8.0.0
sortOn' :: Ord b => (a -> b) -> [a] -> [a]
sortOn' f =
  map snd . sortBy (comparing fst) . map (\x -> let y = f x in y `seq` (y, x))


Measured memory_bytes: 3068