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 <iostream>
#include <iomanip>
#include <math.h>
#include <map>
#include <list>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <string>
#include <sstream>
#include <string.h>
// #include <limits.h>

#define FOR(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define FORUL(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#define FORULE(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define FOREACH(it, X) for(__typeof((X).begin()) it = (X).begin(); it != (X).end(); it++)
#if defined(_MSC_VER) || __cplusplus > 199711L
#define AUTOVAR(newvar,v) auto newvar = (v)
#else
#define AUTOVAR(newvar,v) __typeof(newvar) r = (v)
#endif
#define PB(x) push_back(x)
#define MP(x,y) make_pair((x),(y))
#define MEMSET(m,v) memset(m,v,sizeof(m))

typedef long long				 ll;
typedef unsigned long long		ull;

#define INTMAX  99999999

#define DEBUG 1

#if DEBUG
#define DOUT cout<<"["<<__LINE__<<"]:"
#else
#define DOUT 0 && cout
#endif

using namespace std;

#define MAX_N (1000*100)
#define MAX_AB (1000*100)

int N;
ull K;
ull numcnt[MAX_N+5];

int main(int argc, char *argv[])
{
	ios::sync_with_stdio(false);

	cin >> N >> K;
	int maxa=0;
	FOR(n,N) {
		int a;
		ull b;
		cin >> a >> b;
		maxa = max(maxa,a);
		numcnt[a]+=b;
	}

	ull k=0;
	int a=0;
	for(a=1;a<=maxa;a++) {
		k+=numcnt[a];
		if(k>=K) {
			break;
		}
	}

	cout << a << endl;

	return 0;
}