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>

int main(void)
{
    size_t n, k;
    scanf("%zu %zu", &n, &k);
    size_t u[100002] = { 0 };
    for (size_t i = 0; i < n; ++i) {
        size_t a, b;
        scanf("%zu %zu", &a, &b);
        u[a - 1] += b;
    }
    size_t t = 0;
    for (size_t i = 0; i < 100001; ++i) {
        t += u[i];
        if (t >= k) {
            printf("%zu\n", i + 1);
            break;
        }
    }
    return 0;
}