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 <string.h>
#include <stdbool.h>
#include <math.h>

int sort (const void * a, const void * b){
    if( *(long long int*)a - *(long long int*)b < 0 )
        return -1;
    if( *(long long int*)a - *(long long int*)b > 0 )
        return 1;
    return 0;
}

int main(void){
    long long n,k;
    scanf("%lld%lld",&n,&k);
    long long a[n],b[n],count[100005],anscount=0;
    for (int i=0; i<100005; i++){
        count[i]=0;
    }
    for (long long i=0; i<n; i++){
        scanf("%lld%lld",&a[i],&b[i]);
        count[a[i]]+=b[i];
    }
    qsort (a,n,sizeof(long long),sort);
    
    for (long long i=0; i<n; i++){
        if (i==0 || a[i]!=a[i-1]){
            anscount+=count[a[i]];
        }
        if (anscount>=k){
            printf ("%lld\n",a[i]);
            break;
        }
    }
	return 0 ;
}