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 Rust (1.42.0) (judge verdict: Accepted)

use proconio::{input, fastout};
use std::collections::BTreeMap;

#[fastout]
fn main() {
    input! {
        n: usize, k: usize,
        arr: [(usize, usize); n],
    }

    let mut bmap: BTreeMap<usize, usize> = BTreeMap::new();
    for (a,b) in arr {
        if let Some(x) = bmap.get_mut(&a) {
            *x += b;
        } else {
            bmap.insert(a, b);
        }
    }

    let mut j = 0;
    for (a, b) in bmap {
        j += b;
        if j>=k { println!("{}", a); break; }
    }
}