import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

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


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


l = 0
r = 10 ** 9 + 2
while r - l > 1:
    m = (r + l) // 2
    if C(m):
        r = m
    else:
        l = m
print(r)