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

#define rep(i, a, b) for(int i = (a); i < (b); ++i)
#define all(x) begin(x), end(x)
typedef long long ll;
typedef pair<int, int> pii;
const int inf=1010001000;
const ll  INF=1001000100010001000;
const int mod=(int)1e9+7;

int main(){
    ll n,k;
    cin>>n>>k;
    vector<vector<int>>a(n,vector<int>(2));
    vector<ll>v(n+1,0);
    rep(i,0,n){
        cin>>a[i][0]>>a[i][1];
    }
    sort(all(a));
    rep(i,0,n){
        v.at(i+1)=a[i][1]+v.at(i);
    }
    rep(i,0,n+1){
        if(k<=v.at(i)){
            cout<<a[i-1][0]<<endl;
            return 0;
        }
    }
return 0;
}