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 <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<string> vs;
typedef pair<int, int> P;

#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()

void YN(bool flg){if(flg) cout << "YES" << endl; else cout << "NO" << endl;}
void Yn(bool flg){if(flg) cout << "Yes" << endl; else cout << "No" << endl;}
void yn(bool flg){if(flg) cout << "yes" << endl; else cout << "no" << endl;}

int main()
{
    int n, k;
    cin >> n >> k;
    map<ll, ll> m; 
    rep(i, n) {
        int a, b;
        cin >> a >> b;
        m[a] += b;
    }
    ll cnt = 0;
    int ans = 0;
    for(auto x : m) {
        cnt += x.second;
        if(cnt >= k) {
            ans = x.first;
            break;
        } 
    }

    cout << ans << endl;

    return 0;
}