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 <stdlib.h>
#include <stdio.h>
#define REP(i, n) for(i = 0; i < n; ++i)
#define FOR(i, a, b) for(i = a; i < b; ++i)

typedef struct{
    int a;
    int b;
}nums;

void yes_or_no(char boolean){
    if(boolean){
        printf("Yes\n");
    }else{
        printf("No\n");
    }
}

int comp(const void * a, const void * b){
    nums s_a = *(nums*)a, s_b = *(nums*)b;
    return s_a.a - s_b.a;
}

int main(){
    int i, N;
    long int K;
    scanf("%d %ld", &N, &K);
    nums x[N];
    int ans = 0;
    REP(i, N){
        scanf("%d %d", &x[i].a, &x[i].b);
    }
    qsort(x, N, sizeof(nums), comp);
    REP(i, N){
        K -= x[i].b;
        if(K <= 0){
            ans = x[i].a;
            break;
        }
    }
    printf("%d\n", ans);
    return 0;
}