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: Wrong Answer)

use proconio::input;
fn main() {
    input! {
        n: usize,
        k: usize,
    }
    let mut a: Vec<usize> = vec![];
    let mut b: Vec<usize> = vec![];

    for i in 0..n {
        input! {
            an: usize,
            bn: usize
        }
        a.push(an);
        if i == 0 {
            b.push(bn);
        } else {
            b.push(b[i - 1] + bn);
        }
    }

    let mut res = 0;
    for i in 0..n {
        if k <= b[i] {
            res = a[i];
            break;
        }
    }

    println!("{}", res);
}