{-# OPTIONS_GHC -O2 -funbox-strict-fields #-}
{-# LANGUAGE BangPatterns      #-}
{-# LANGUAGE CPP               #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TupleSections     #-}

import           Control.Applicative
import           Control.Monad
import           Control.Monad.Primitive
import           Control.Monad.ST
import           Control.Monad.State.Strict
import           Data.Bool
import qualified Data.ByteString.Char8       as B
import qualified Data.ByteString.Unsafe      as B
import           Data.Char
import           Data.Function
import qualified Data.IntMap.Strict          as IM
import qualified Data.IntSet                 as IS
import           Data.List
import qualified Data.Map.Strict             as M
import           Data.Monoid
import           Data.Ord
import           Data.Primitive.MutVar
import qualified Data.Set                    as S
import           Data.Tuple
import qualified Data.Vector                 as V
import qualified Data.Vector.Generic         as G
import qualified Data.Vector.Generic.Mutable as GM
import qualified Data.Vector.Unboxed         as U
import qualified Data.Vector.Unboxed.Mutable as UM
import           Debug.Trace
import           Foreign                     hiding (void)
import           Unsafe.Coerce

main :: IO ()
main = do
    !n <- readLn :: IO Int
    xs <- U.unfoldrN n (B.readInt.B.dropWhile isSpace) <$> B.getLine
    print $ solve xs `mod` modulus

modulus :: Int
modulus = 1000000007

solve :: U.Vector Int -> Int
solve xs = go 1 1 1 . tail  $ U.toList xs
  where
    go !acc !len !prev (cur:xs)
      | cur-prev == 1 = go (acc * (len+1) `rem` modulus) len prev xs
      | otherwise = go acc (len+1) (prev+2) xs
    go acc len _ _ = foldl' (\acc x->acc*x`rem`modulus) acc [1..len]