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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<cstdio>
#include<vector>
#include<algorithm>

#define rep(n) for(int i=0;i<n;i++)
#define Pii std::pair<int, int>
#define all(v) v.begin(), v.end()

int main(){
    int length = 0, n, k;
    scanf("%d %d", &n, &k);
    std::vector<Pii> v(n);
    rep(n) scanf("%d %d", &v[i].first, &v[i].second);
    std::sort(all(v));
    for(Pii p: v){
        if(length < k && k <= length+p.second){
            printf("%d\n", p.first);
            return 0;
        }
        length += p.second;
    }
}