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::*;

fn main() {
    let stdin = std::io::stdin();
    let mut reader = std::io::BufReader::new(stdin.lock());
    let mut s = String::new();
    reader.read_line(&mut s).unwrap();
    let mut iter = s.split_whitespace();
    let n: usize = iter.next().unwrap().parse().unwrap();
    let mut k: usize = iter.next().unwrap().parse().unwrap();

    let mut arr = vec![];
    for _ in 0..n {
        let mut s = String::new();
        reader.read_line(&mut s).unwrap();
        let mut iter = s.split_whitespace();
        let a: usize = iter.next().unwrap().parse().unwrap();
        let b: usize = iter.next().unwrap().parse().unwrap();
        arr.push((a, b));
    }
    arr.sort();

    for (a, b) in arr {
        if k <= b {
            println!("{}", a);
            break;
        }
        k -= b;
    }
}