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 ll long long
int main()
{
    ll n,i,j,k,l,a,b,c,s;
    cin>>n>>k;
    vector<ll>vc;
    map<ll,ll>mp;
    for(i=0;i<n;i++)
    {
        cin>>a>>b;
        if(mp[a]==0)
        {
            vc.push_back(a);
            mp[a]=mp[a]+b;
        }
        else if(mp[a]!=0)
        {
            mp[a]=mp[a]+b;
        }
    }
    sort(vc.begin(),vc.end());
    i=0;
    s=0;
    while(s<k)
    {
        l=vc[i];
        j=mp[l];
        s+=j;
        i++;
    }
    cout<<l<<endl;
    return 0;

}