Problem:
Score : 400 points

Problem Statement

You are going out for a walk, when you suddenly encounter a monster. Fortunately, you have N katana (swords), Katana 1, Katana 2, …, Katana N, and can perform the following two kinds of attacks in any order:

Wield one of the katana you have. When you wield Katana i (1 ≤ i ≤ N), the monster receives a_i points of damage. The same katana can be wielded any number of times.

Throw one of the katana you have. When you throw Katana i (1 ≤ i ≤ N) at the monster, it receives b_i points of damage, and you lose the katana. That is, you can no longer wield or throw that katana.

The monster will vanish when the total damage it has received is H points or more. At least how many attacks do you need in order to vanish it in total?

Constraints

1 ≤ N ≤ 10^5

1 ≤ H ≤ 10^9

1 ≤ a_i ≤ b_i ≤ 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

N H
a_1 b_1
:
a_N b_N

Output

Print the minimum total number of attacks required to vanish the monster.

Sample Input 1

1 10
3 5

Sample Output 1

3

You have one katana. Wielding it deals 3 points of damage, and throwing it deals 5 points of damage. By wielding it twice and then throwing it, you will deal 3 + 3 + 5 = 11 points of damage in a total of three attacks, vanishing the monster.

Sample Input 2

2 10
3 5
2 6

Sample Output 2

2

In addition to the katana above, you also have another katana. Wielding it deals 2 points of damage, and throwing it deals 6 points of damage. By throwing both katana, you will deal 5 + 6 = 11 points of damage in two attacks, vanishing the monster.

Sample Input 3

4 1000000000
1 1
1 10000000
1 30000000
1 99999999

Sample Output 3

860000004

Sample Input 4

5 500
35 44
28 83
46 62
31 79
40 43

Sample Output 4

9

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Applicative
import Control.Monad
import Control.Monad.ST
import Data.Functor
import Data.Function
import Data.Monoid
import Data.Maybe
import Data.List
import qualified Data.Foldable as Foldable
import qualified Data.Set as Set
import qualified Data.Sequence as Sequence
import Data.List.Split
import Data.Bits
import Data.Char
import Data.Ix
import Data.Ratio
import Data.Ord
import Data.Tuple
--import Data.Array
import Data.Array.IArray
--import Data.Array.Unboxed
import Data.Array.MArray
import Data.Array.IO
import Data.Array.ST
import Data.IORef
import Data.STRef
-- import System.IO.Unsafe
 
readInt = read :: String -> Int
readInteger = read :: String -> Integer
readDouble = read :: String -> Double
getInt = readLn :: IO Int
getInts = map readInt . words <$> getLine
getInteger = readLn :: IO Integer
getIntegers = map readInteger . words <$> getLine
getDouble = readLn :: IO Double
sjoin :: (Show a) => [a] -> String
sjoin = unwords . map show
cond :: a -> a -> Bool -> a
cond t f c = if c then t else f
apply2 :: (a -> a -> b) -> [a] -> b
apply2 f [x,y] = f x y
apply3 :: (a -> a -> a -> b) -> [a] -> b
apply3 f [x,y,z] = f x y z
apply4 :: (a -> a -> a -> a -> b) -> [a] -> b
apply4 f [x,y,z,w] = f x y z w
fnBin :: (b -> c -> d) -> (a -> b) -> (a -> c) -> a -> d
fnBin op f g x = op (f x) $ g x
fnTuple :: (a -> b, a -> c) -> a -> (b, c)
fnTuple (f,g) a = (f a, g a)
replace :: (Eq a) => a -> a -> [a] -> [a]
replace x y = map (\z -> if z==x then y else z)
modifyArray :: (Ix i, MArray a e m) => a i e -> i -> (e -> e) -> m ()
modifyArray arr ix f = readArray arr ix >>= writeArray arr ix . f
dictCompare :: [a -> a -> Ordering] -> a -> a -> Ordering
dictCompare [] _ _ = EQ
dictCompare (f:fs) x y = let c = f x y in if c==EQ then dictCompare fs x y else c
binMap :: (a -> a -> b) -> [a] -> [b]
binMap f (x:xs@(y:_)) = f x y : binMap f xs
binMap _ _ = []
splitRec :: Int -> [a] -> [[a]]
splitRec _ [] = []
splitRec n xs = let (y,ys) = splitAt n xs in y : splitRec n ys
infixl 7 `divCeil`
divCeil :: Integral a => a -> a -> a
x `divCeil` y = (x+y-1) `div` y
-- end of templete


main = do
    [n,h] <- getInts
    xs <- map (apply2 (,)) <$> replicateM n getInts
    print $ let da = maximum $ map fst xs in let fd = scanl (-) h $ sortBy (flip compare) $ filter (>=da) $ map snd xs in let r = last fd in if r>0 then length fd - 1 + r `divCeil` da else length $ filter (>0) fd