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: Accepted)

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
const int MaxN = 1e5;
using namespace std;

struct NODE{
	int w , v;
}a[MaxN + 5];
int n ;
long long k;
bool cmp(NODE x , NODE y){
	return x.w < y.w;
}
int main()
{
	while(~scanf("%d%lld" , &n , &k)){
		for(int i = 1;i <= n;i++){
			scanf("%d%d" , &a[i].w , &a[i].v);
		}
		sort(a + 1 , a + n + 1 , cmp);
		long long  f = 1 , e = a[1].v;
		for(int i = 2;i <= n + 1;i++){
			if(k >= f && k <= e) {
				printf("%d\n" , a[i - 1].w);
				break;
			}
			else f = e + 1 , e = e + a[i].v;
		}
	}
}