import sys

input = sys.stdin.readline

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

ok = 10**9
ng = 0
for _ in range(30):
    mid = (ok + ng) // 2
    tmp = 0
    for a, b in operation:
        if mid < a:
            continue
        tmp += min(b, mid) - a + 1
    if tmp >= k:
        ok = mid
    else:
        ng = mid

print(ok)