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)

#![allow(unused)]

use std::cmp::{max, min};
use std::io::stdin;
use std::str::FromStr;

fn input<T: FromStr>() -> Result<T, T::Err> {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    buf.trim().parse()
}

fn input_vec<T: FromStr>() -> Result<Vec<T>, T::Err> {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    buf.trim().split_whitespace().map(|x| x.parse()).collect()
}

use std::collections::HashMap;

fn main() {
    let (n, k): (usize, usize) = {
        let v = input_vec().unwrap();
        (v[0], v[1])
    };

    let ab: Vec<(usize, usize)> = {
        let mut res = Vec::new();
        for i in 0..n {
            let v = input_vec().unwrap();
            res.push((v[0], v[1]));
        }
        res
    };

    // set[i]はiを挿入する数
    let mut set: HashMap<usize, usize> = HashMap::new();

    for (a, b) in ab {
        let h = set.entry(a).or_insert(0);
        *h += b;
    }

    // println!("{:?}", set);
    let mut v = set.iter().collect::<Vec<_>>();
    v.sort();
    let mut accu = 0usize;
    for (a, b) in v {
        if accu + b >= k {
            println!("{}", a);
            break;
        } else {
            accu += *b;
        }
    }
}