from collections import defaultdict as dd

n, k = map(int, input().split())
ab = [tuple(map(int, input().split())) for _ in range(n)]

cnts = dd(int)
for a, b in ab:
    cnts[a] += 1
    cnts[b + 1] -= 1

cnt = 0
acc = 0
cnts = [(key, val) for key, val in sorted(cnts.items())]
m = len(cnts)
for i in range(m - 1):
    acc += cnts[i][1]
    if cnt + acc * (cnts[i + 1][0] - cnts[i][0]) > k:
        ans = cnts[i][0] + (k - cnt + acc - 1) // acc - 1
        print(ans)
        exit()

    cnt += acc * (cnts[i + 1][0] - cnts[i][0])