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 Data.List
import Data.Function
import Data.Maybe
import qualified Data.ByteString.Char8 as BC8

main :: IO ()
main = do
  [n, k] <- (map read . words) <$> getLine :: IO [Int]
  -- rows <- replicateM n $ map (fst . fromJust . BC8.readInt) . BC8.words <$> BC8.getLine :: IO [[Int]]
  rows <- replicateM n $ (map read . words) <$> getLine :: IO [[Int]]
  let sorted = sortBy (compare `on` head) rows
  print =<< solve k 0 0 sorted

solve k i a' rows
  | k <= i = return a'
  | otherwise = let [a, b]:rows' = rows in solve k (i + b) a rows'