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<string>
#include<iostream>
#include<algorithm>
#include<set>
#include<math.h>
#include<vector>
#include<sstream>
#include<queue>
#include<functional>
#include<bitset>
#include<cstdio>
#include<iomanip>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include <string.h>
using ll = long long;

#define rep(i, n) for(ll i = 0; i < (int)(n); i++)
#define reps(i,x) for(ll i=1;i<=(int)(x);i++)
#define rrep(i,x) for(ll i=((int)(x)-1);i>=0;i--)
#define rreps(i,x) for(ll i=((int)(x) - 1 * 100);i>0;i--)
#define all(x) (x).begin(),(x).end()
#define m0(x) memset(x,0,sizeof(x))
#define vll vector<ll>
#define vi vector<int>
#define mp make_pair
#define vpll vector<pair<ll,ll>>
#define vpi vector<pair<int,int>>
using namespace std;
ll n,k;
ll a[100000];
int main() {
	cin >> n >> k;
	map<ll, ll> mp;
	ll t1, t2;
	rep(i, n) {
		cin >> t1 >> t2;
		mp[t1] += t2;
	}
	ll sum = 0;
	for (auto kv : mp) {
		sum += kv.second;
		if (sum >= k) {
			cout << kv.first << endl;
			return 0;
		}
	}
	return 0;
}