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: Accepted)

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

#define MAX_N (100000)
#define rep(i, n) for(int64_t i = 0; i < (n); i++)

typedef struct {
  int A;
  int B;
} st_nums;

int nums_sort(const void *a, const void *b) {
  return (((st_nums*)a)->A - ((st_nums*)b)->A);
}

int main(void) {
  int64_t N, K;
  scanf("%ld %ld", &N, &K);

  st_nums NUM[MAX_N];
  rep(i, N) {
    scanf("%d %d", &NUM[i].A, &NUM[i].B);
  }
  qsort(NUM, N, sizeof(st_nums), nums_sort);

  int64_t ANS;
  int64_t SUM = 0;
  rep(i, N) {
    SUM += NUM[i].B;
    if(SUM >= K) {
      ANS = NUM[i].A;
      break;
    }
  }
  printf("%ld\n", ANS);
  return 0;
}