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: Time Limit Exceeded)

import Control.Applicative
import Data.List
import qualified Data.Set as Set

main = do
    [n,k] <- map read . words <$> getLine  :: IO [Int]
    list <- sequence (replicate n ((\[x,y]->(x,y)) . map read . words <$> getLine)) :: IO [(Int,Int)]
    print $ solve k list

solve :: Int -> [(Int,Int)] -> Int
solve k list = (sort ( f list)) !! (k-1)

f :: [(Int,Int)] -> [Int]
f [] = []
f ((a,b):xs) =  append a b (f xs)

append :: a -> Int -> [a] -> [a]
append _ 0 list = list
append x n list = append x (n-1) (x:list)