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


def cnt(x):
    res = 0
    for a, b in AB:
        if a <= x:
            res += min(b, x) - a + 1
    return res


# bisect
l, r = 0, 10 ** 9 + 1
while r - l > 1:
    m = (r + l) // 2
    if cnt(m) < K:
        l = m
    else:
        r = m
print(r)