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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<stdlib.h>

int compr(const void *ax, const void *ay){
	unsigned long *x = *(unsigned long **)ax;
	unsigned long *y = *(unsigned long **)ay;

	if(x[0] > y[0]) return 1;
	if(x[0] < y[0]) return -1;
	if(x[0] = y[0]) return 0;
}

unsigned long answer(unsigned int N, unsigned long long K, unsigned long *a, unsigned long *b){
	unsigned long **list, k = 0, rtn;
	unsigned int i;

	list  = (unsigned long **)malloc(sizeof(unsigned long *)*N);
	if(list == NULL) exit(1);
	for(i = 0; i < N; i++){
		list[i] = (unsigned long *)malloc(sizeof(unsigned long)*2);
		if(list[i] == NULL) exit(1);
		list[i][0] = a[i];
		list[i][1] = b[i];
	}

	qsort(list, N, sizeof(unsigned long *), compr);
	for(i = 0; i < N; i++){
		k += list[i][1];
			rtn = list[i][0];
		if(k >= K){
			break;
		}
	}
	
	for(i = 0; i < N; i++) free(list[i]);
	free(list);
	return rtn;
}

int main(){
	unsigned int N, i;
	unsigned long *a, *b;
	unsigned long long K;
	char line[16];

	fgets(line, 16, stdin);
	sscanf(line, "%ld %llu", &N, &K);

	a = (unsigned long *)malloc(sizeof(unsigned long)*N);
	b = (unsigned long *)malloc(sizeof(unsigned long)*N);
	if((a == NULL) || (b == NULL)) exit(1);

	for(i = 0; i < N; i++){
		fgets(line, 16, stdin);
		sscanf(line, "%lu %lu", &a[i], &b[i]);
	}

	printf("%lu\n", answer(N, K, a, b));

	free(a);
	free(b);
	return 0;
}