from sys import stdin, exit
##  input functions for me
def ria(sep = ''):
    if sep == '' :
        return list(map(int, input().split())) 
    else: return list(map(int, input().split(sep)))
def rsa(sep = ''):
    if sep == '' :
        return input().split() 
    else: return input().split(sep)
def ri(): return int(input())
def rd(): return float(input())
def rs(): return input()
##

## main ##
N, K = map(int, input().split())
A = [0] * N
B = [0] * N
for i in range(N): A[i], B[i] = map(int, input().split())

l = set()
for i in range(N):
    l.add(A[i])
    l.add(B[i])
    l.add(A[i] + 1)
    l.add(B[i] + 1)
    l.add(A[i] - 1)
    l.add(B[i] - 1)

ll = list(l)
ll.sort()
d = dict()
idx = 0
for n in ll:
    d[n] = idx
    idx += 1

NN = len(d)
imos = [0] * (NN + 1)
for i in range(N):
    imos[d[A[i]]] += 1
    imos[d[B[i]] + 1] += -1

sum = [0] * (NN + 1)
for i in range(NN):
    sum[i] = imos[i]
    if i > 0 : sum[i] += sum[i - 1]
#print(ll)
#print(sum)

tot = 0
for i in range(NN - 1):
    ntot = tot + sum[i] * (ll[i + 1] - ll[i])
    if ntot < K:
        tot = ntot
        continue
    rest = K - tot
    mm = (rest + sum[i] - 1) // sum[i]
    print(ll[i] + mm - 1)
    exit()