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

merge :: [(Int, Int)] -> [(Int, Int)] -> [(Int, Int)]
merge xs [] = xs
merge [] ys = ys
merge (x:xs) (y:ys)
    | fst x < fst y = x : merge xs (y:ys)
    | otherwise     = y : merge (x:xs) ys

msort :: [(Int, Int)] -> [(Int, Int)]
msort [] = []
msort [x] = [x]
msort x = merge (msort (take h x)) (msort (drop h x))
    where
        h = length x `div` 2

minus :: Int -> Int -> Int
n `minus` m = if n - m <= 0 then 0 else n - m

getN :: Int -> [(Int, Int)] -> Int
getN 0 (x:xs) = fst x
getN n (x:xs) = if n `minus` snd x == 0 then fst x else getN (n `minus` snd x) xs


main = do
  [n, k] <- map read . words <$> getLine
  numPares <- replicateM n $ do
                [p, q] <- map read . words <$> getLine
                return (p,q)
                
  putStrLn $ show $ getN k (msort numPares)