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::io::*;
use std::str::FromStr;

pub fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

use std::cmp::max;
use std::cmp::Ordering;

fn main() {
    let n: usize = read();
    let mut k: usize = read();
    let mut vec: Vec<(i64, i64)> = vec![];
    for _ in 0..n {
        let a: i64 = read();
        let b: i64 = read();
        vec.push((a, b))
    }
    vec.sort_by(|a, b| {
        if a.0 > b.0 {
            return Ordering::Greater;
        } else {
            if a.0 == b.0 {
                return Ordering::Equal;
            }
            return Ordering::Less;
        }
    });

    for i in 0..n {
        let vi = vec[i];
        if k <= vi.1 as usize {
            println!("{}", vi.0);
            return;
        }
        k -= vi.1 as usize;
    }
}