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<cstdio>
#include<bits/stdc++.h>
typedef long long int ll;
#define REP(i, n) for(int i = 0; i < (n); i++)
#define FOR_IN(i, a, b) for(int i = (a); i < (b); i++)
#define BETWEEN(x, a, b) ((x) >= (a) && (x) <= (b))
#define BIT(b, i) (((b) >> (i)) & 1)
#define LOG_F 1
#define LOG(...) if(LOG_F) fprintf(stderr, __VA_ARGS__)

using namespace std;

ll pow(int x, int n){
  return n == 0 ? 1 : x * pow(x, n - 1);
}


/*
n k
ai bi

n a b 10^5
k b1+...+bn

*** use ll!!! ***
 */
typedef pair<int,int> P;
int n,k;
P ps[100000];

int main(){
  cin>>n>>k;
  
  REP(i,n){
    int a,b;
    cin>>a>>b;
    ps[i] = P(a,b);
  }

  sort(ps, ps+n);

  int i;
  ll cnt=0;  
  for(i=0; i<n; i++){
    cnt += ps[i].second;
    if(cnt >= k){
      cout<<ps[i].first<<endl;
      return 0;
    }
  }

  return 0;
}