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


def is_ok(x):
    cnt = 0
    for a, b in ab:
        cnt += max(0, min(x, b) - a + 1)

    return k <= cnt


ok, ng = 10**9, 0
while ok - ng > 1:
    m = (ok + ng) // 2
    if is_ok(m):
        ok = m
    else:
        ng = m

print(ok)