from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

N,K = map(int,input().split())
AB = [tuple(map(int,input().split())) for _ in range(N)]

def is_ok(x):
    
    tmp = 0
    for a,b in AB:
        if x<a:
            continue
        elif x<=b:
            tmp += x-a+1
        else:
            tmp += b-a+1
    return tmp>=K
    
x = 0
y = 10**9 
while y-x>1:
    mid = (y+x)//2
    if is_ok(mid):
        y = mid
    else:
        x = mid
print(y)