Problem:
Score : 300 points

Problem Statement

There is an empty array.
The following N operations will be performed to insert integers into the array.
In the i-th operation (1≤i≤N), b_i copies of an integer a_i are inserted into the array.
Find the K-th smallest integer in the array after the N operations.
For example, the 4-th smallest integer in the array \{1,2,2,3,3,3\} is 3.

Constraints

1≤N≤10^5

1≤a_i,b_i≤10^5

1≤K≤b_1…+…b_n

All input values are integers.

Input

Input is given from Standard Input in the following format:

N K
a_1 b_1
:
a_N b_N

Output

Print the K-th smallest integer in the array after the N operations.

Sample Input 1

3 4
1 1
2 2
3 3

Sample Output 1

3

The resulting array is the same as the one in the problem statement.

Sample Input 2

10 500000
1 100000
1 100000
1 100000
1 100000
1 100000
100000 100000
100000 100000
100000 100000
100000 100000
100000 100000

Sample Output 2

1

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

import Control.Monad
import Control.Applicative
import Data.List
import qualified Data.Map as Map
import Data.Array
import qualified Data.ByteString.Char8 as BC
import Data.Maybe
import qualified Data.Set as Set
import qualified Data.Sequence as Sq
import qualified Data.IntMap as IMap
import qualified Data.Vector as V
import Data.Sequence (ViewL(..),ViewR(..),(><),(<|),(|>),Seq)

bsreadInt :: BC.ByteString -> Int
bsreadInt = fst . fromJust . BC.readInt

sqleft :: Seq a -> a
sqleft q = sqleft_(Sq.viewl q)
sqleft_ :: ViewL a -> a
sqleft_ (x :< xs) = x
sqright :: Seq a -> a
sqright q = sqright_(Sq.viewr q)
sqright_ :: ViewR a -> a
sqright_ (xs :> x) = x

-------------------------------------------------------------
count :: [[Int]] -> Int -> Int -> Int
count (c:cn) n k = if (n + b) >= k
                   then a
                   else count cn (n+b) k
                   where a = c !! 0
                         b = c !! 1

main = do
    [n,k] <- map bsreadInt . BC.words <$> BC.getLine
    abin <- map ((map bsreadInt . BC.words)) <$> replicateM n BC.getLine
    let ab = sort abin
    print $ count ab 0 k