monotonic :: [Int] -> Bool
monotonic xs = all (<0) xs || all (>0) xs

gradual :: [Int] -> Bool
gradual = all ((<= 3) . abs)

differences :: [Int] -> [Int]
differences (x:y:xs) = x-y : differences (y:xs)
differences _ = []

safe :: [Int] -> Bool
safe xs = let ys = differences xs
  in monotonic ys && gradual ys

safe' :: [Int] -> Bool
safe' = any safe . removals

line :: String -> Bool
line = safe' . map read . words

count :: (a -> Bool) -> [a] -> Int
count p = foldr f 0
  where
    f x y = if p x then succ y else y

remove :: Int -> [a] -> [a]
remove n xs = take n xs ++ drop (n+1) xs

removals :: [a] -> [[a]]
removals xs = map (flip remove xs) [0..length xs - 1]

main :: IO ()
main = do
  s <- getContents
  let ls = lines s
  let xs = map line ls
  print $ count id xs