main :: IO()
main = do
    _ <- readLn
    ls <- map read . words <$> getLine
    putStrLn $ if getsolve ls then "Yes" else "No"
    
    
getsolve :: [Int] -> Bool
getsolve ls
    | length ls == 1		= True
    | a > b+1				= False
    | otherwise				= getsolve $ tail ls
    where a = ls!!0
          b = ls!!1