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 Python (3.4.3) (judge verdict: Accepted)

import sys
n,k=map(int,input().split())
s=[]
tmp_a=[]
tmp=0
for i in range(n):
    a,b=map(int,input().split())
    tmp_a.append(a)
    s.append([a,b])#aをb個挿入する
s.sort()
tmp1_a=set(tmp_a)
sS=[]
s_sum=s[0][1]
for i in range(1,n):
    if s[i-1][0]==s[i][0]:
        s_sum+=s[i][1]
    else:
        sS.append([s[i-1][0],s_sum])
        s_sum=0
        s_sum+=s[i][1]
    if i==(n-1):
        sS.append([s[i][0],s_sum])
for i in range(len(tmp1_a)):
    tmp+=sS[i][1]
    if tmp>=k:
        print(sS[i][0])
        break