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_imports)]
    use std::cmp::{max, min, Ordering};
    #[allow(unused_imports)]
    use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
    #[allow(unused_imports)]
    use std::iter::FromIterator;
    // input macro
    // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
    macro_rules! input {
        (source = $s:expr, $($r:tt)*) => {
            let mut iter = $s.split_whitespace();
            let mut next = || { iter.next().unwrap() };
            input_inner!{next, $($r)*}
        };
        ($($r:tt)*) => {
            let stdin = std::io::stdin();
            let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
            let mut next = move || -> String{
                bytes
                    .by_ref()
                    .map(|r|r.unwrap() as char)
                    .skip_while(|c|c.is_whitespace())
                    .take_while(|c|!c.is_whitespace())
                    .collect()
            };
            input_inner!{next, $($r)*}
        };
    }
     
    macro_rules! input_inner {
        ($next:expr) => {};
        ($next:expr, ) => {};
     
        ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
            let $var = read_value!($next, $t);
            input_inner!{$next $($r)*}
        };
    }
     
    macro_rules! read_value {
        ($next:expr, ( $($t:tt),* )) => {
            ( $(read_value!($next, $t)),* )
        };
     
        ($next:expr, [ $t:tt ; $len:expr ]) => {
            (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
        };
     
        ($next:expr, chars) => {
            read_value!($next, String).chars().collect::<Vec<char>>()
        };
     
        ($next:expr, usize1) => {
            read_value!($next, usize) - 1
        };
     
        ($next:expr, $t:ty) => {
            $next().parse::<$t>().expect("Parse error")
        };
    }
     
    fn main() {
        input!{
            n: usize,
            k: i64,
            ab: [(usize, i64); n],
        }
        let mut v = vec![0; 100010];
        for (a, b) in ab {
            v[a] += b;
        }
        let mut count = 0;
        //let ans:usize;
        for i in (0..100010) {
            count += v[i];
            if count >= k {
                println!("{}", i);
                break;
            }
        }
    }