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: Accepted)

use std::collections::HashMap;

fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let v: Vec<usize> = s.trim().split_whitespace().map(|x| x.parse().unwrap()).collect();
    let mut h: HashMap<usize, usize> = HashMap::new();
    for _ in 0..v[0] {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).unwrap();
        let u: Vec<usize> = s.trim().split_whitespace().map(|x| x.parse().unwrap()).collect();
        let x = match h.get(&u[0]) {Some(x) => *x, None => 0};
        h.insert(u[0], x + u[1]);
    }
    let mut k = h.keys().collect::<Vec<&usize>>();
    k.sort();
    let mut x = 0;
    for i in &k {
        x += *h.get(*i).unwrap();
        if x >= v[1] {println!("{}", *i); return}
    }
}