from bisect import bisect
from itertools import accumulate

N, K = map(int, input().split())
D = {0}
AB = []
for _ in range(N):
    a, b = map(int, input().split())
    D.add(a)
    D.add(b + 1)
    AB.append((a, b + 1))
D = sorted(list(D))
ND = len(D)
dic = dict(zip(D, range(ND)))
X = [0] * (ND + 1)
for a, b in AB:
    X[dic[a]] += 1
    X[dic[b]] -= 1
X = list(accumulate(X))
Y = [0] * ND
for i in range(1, ND):
    Y[i] = Y[i - 1] + X[i - 1] * (D[i] - D[i - 1] - 1) + X[i]
a = bisect(Y, K) - 1
print(D[a] - ((Y[a] - K) // X[a]))