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>

typedef struct{
    int num;
    int count;
}NC;

int comp(NC *a, NC *b){
    return a->num - b->num;
}
int main(void){
    long long int n, k, pos = 0;
    int i;
    NC nc[100000];
    
    scanf("%lld%lld", &n, &k);
    
    for(i = 0; i < n; i++){
        scanf("%d%d", &nc[i].num, &nc[i].count);
    }
    qsort(nc, n, sizeof(NC), comp);
    
    for(i = 0; i < n; i++){
        if(pos + nc[i].count >= (long long int)k){
            printf("%d\n", nc[i].num);
            break;
        }
        pos += (long long int)nc[i].count;
    }
    return 0;
}