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::fmt::Debug;
use std::io;
use std::io::{Read, Stdin};
use std::str;
use std::str::FromStr;

fn main() {
    let mut sc = Scanner::new();
    let n = sc.parse();
    let k = sc.parse();
    let ab = sc.pairs(n);
    println!("{}", solve(ab, k));
}


fn solve(ab: Vec<(usize, u32)>, k: i64) -> u32 {
    let mut counter = [0; 100001];
    for p in ab {
        counter[p.0] += p.1;
    }
    let mut k = k;
    let mut last_i = 0;
    for i in 0..100001 {
        let n = counter[i];
        if n != 0 {
            k -= n as i64;
            if k <= 0 {
                return i as u32;
            }
            last_i = i;
        }
    }
    last_i as u32
}

#[test]
fn test() {
    assert_eq!(2, solve(vec![(1, 1), (2, 2), (3, 3)], 3));
    assert_eq!(3, solve(vec![(1, 1), (2, 2), (3, 3)], 4));
    assert_eq!(1,
               solve(vec![(1, 100000),
                          (1, 100000),
                          (1, 100000),
                          (1, 100000),
                          (1, 100000),
                          (100000, 100000),
                          (100000, 100000),
                          (100000, 100000),
                          (100000, 100000)],
                     500000));
}

struct Scanner {
    stdin: Stdin,
    buf: Vec<u8>,
}

impl Scanner {
    fn new() -> Scanner {
        Scanner {
            stdin: io::stdin(),
            buf: Vec::with_capacity(256),
        }
    }

    fn parse<T: FromStr>(&mut self) -> T
        where <T as FromStr>::Err: Debug
    {
        self.buf.clear();
        let mut it = self.stdin.lock().bytes();
        let mut c = it.next().unwrap().unwrap();
        while c == ' ' as u8 || c == '\n' as u8 {
            c = it.next().unwrap().unwrap();
        }
        while !(c == ' ' as u8 || c == '\n' as u8) {
            self.buf.push(c);
            c = it.next().unwrap().unwrap();
        }
        str::from_utf8(&self.buf).unwrap().parse::<T>().unwrap()
    }

    fn pairs<A: FromStr, B: FromStr>(&mut self, n: usize) -> Vec<(A, B)>
        where <A as FromStr>::Err: Debug,
              <B as FromStr>::Err: Debug
    {
        (0..n).map(|_| (self.parse(), self.parse())).collect()
    }
}