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 (1.15.1) (judge verdict: Runtime Error)

use std::io::stdin;

#[allow(dead_code)]
fn input_strs() -> Vec<char> {
    let mut s = String::new();
    match stdin().read_line(&mut s) {
        Ok(_) => s.chars().collect(),
        Err(_) => panic!("err"),
    }
}

#[allow(dead_code)]
fn input_ints() -> Vec<u32> {
    let mut st = String::new();
    match stdin().read_line(&mut st) {
        Ok(_) => st.split_whitespace().map(|s| s.parse().unwrap()).collect(),
        Err(_) => panic!("err"),
    }
}

#[allow(unused_variables)]
fn solve() {
    let l = input_ints();
    let n = l[0] as usize;
    let k = l[1];

    let mut v = Vec::<(u32, u32)>::with_capacity(n);

    for _ in 0..n {
        let l = input_ints();
        v.push((l[0], l[1]));
    }

    v.sort_by_key(|&(a, b)| a);

    let mut cnt = 0;

    for (a, b) in v {
        cnt += b;
        if k <= cnt {
            println!("{}", a);
            break;
        }
    }
}

fn main() {
    solve();
}