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)

#pragma GCC optimize("Ofast")
  
#include <iostream>
#include <algorithm>
#include <vector>
#include <cstring>
#include <string>
#include <map>
#include <unordered_map>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <unordered_set>
#include <list>
#include <tuple>
#include <iomanip>
#include <climits>
#include <cstdlib>
#include <cassert>
#include <numeric>
#include <cmath>
#include <bitset>
#include <random>
#include <regex>

using namespace std;
  
#define rep(i,n) for(int i=0;i<(n);++i)
#define reps(i,n) for(int i=1;i<=(n);++i)
#define all(x) (x).begin(),(x).end()
#define Fixed fixed << setprecision(14)
#define int int64_t
using pii = pair<int,int>;
constexpr int INF  = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr int mod1 = 1e9+7; 
constexpr int mod2 = 998244353;
constexpr int dy[] = {0,1,0,-1,1,-1,-1,1};
constexpr int dx[] = {1,0,-1,0,1,1,-1,-1};
 
template <class A, class B> inline bool chmax(A &a, const B &b) { return b > a && (a = b, true); }
template <class A, class B> inline bool chmin(A &a, const B &b) { return b < a && (a = b, true); }

template <class A, class B> inline A updiv(const A a,const B b){ return (a + b - 1) / b; }
template <class A, class B> inline A gcd(const A a,const B b){ return b ? gcd(b,a % b) : a; }
template <class A, class B> inline A lcm(const A a,const B b){ return a / gcd(a,b) * b; }

template <class T> using min_heap = priority_queue<T,vector<T>,greater<T> >;
template <class T> using max_heap = priority_queue<T>;
template <class A,class B> using umap = unordered_map<A,B>;
    
signed main(void){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    int n, k;
    cin >> n >> k;

    vector<pii> v(n);

    for(auto &e : v){
        cin >> e.first >> e.second;
    }

    sort(all(v));

    int sum = 0;
    for(auto e : v){
        sum += e.second;
        if(k <= sum){
            return cout << e.first << '\n', 0;
        }
    }

    return 0;
}