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;
use std::collections::BTreeMap;

fn main() {
    let mut first = String::new();
    io::stdin().read_line(&mut first);
    let mut fitr = first.split_whitespace();
    let n = fitr.next().unwrap().parse::<i32>().unwrap();
    let k = fitr.next().unwrap().parse::<i32>().unwrap();

    let mut bt = BTreeMap::<i32, i32>::new();
    for _ in 0..n {
        let mut line = String::new();
        io::stdin().read_line(&mut line);
        let mut itr = line.split_whitespace();
        let a = itr.next().unwrap().parse::<i32>().unwrap();
        let b = itr.next().unwrap().parse::<i32>().unwrap();
        
        *bt.entry(a).or_insert(0) += b;
    }

    let mut kmin = 0i32;
    let mut d = k;
    for (key, val) in bt.iter() {
        if d <= *val {
            kmin = *key;
            break;
        }
        d -= *val;
    }

    println!("{}", kmin);
}