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: Runtime Error)

#include <iostream>
#include <cstdio>
#include <queue>
#include <vector>
#include <stack>
#include <string>
#include <tuple>
#include <random>
#include <map>
#include <set>
#include <complex>
#include <algorithm>
#include <cassert>
#include <iterator>
#include <numeric>
#include <cmath>
#include <stdio.h>
#include <functional>

#define REP(i,a) for(int (i)=0;(i)<(a);i++)
#define RREP(i,a,b) for(int (i)=(a);(i)<(b);i++)
#define all(c) (c).begin(),(c).end()
#define sz(v) (int)(v).size()
#define vi vector<int> 
typedef long long ll;
using namespace std;

int main(void){
    ll N,K;
    cin>>N>>K;
    vi a(N),b(N);
    int kosuu[100001];
    REP(i,N){
        cin>>a[i]>>b[i];
        kosuu[a[i]]+=b[i];
    }
    ll tmp=0,ans=1;
    while(1){
        tmp+=kosuu[ans];
        if(tmp>=K)break;
        ans++;
    }
    cout<<ans;
    return 0;
}