import sys
readline = sys.stdin.readline

def check(m):
    cnt = 0
    for i in range(N):
        if m > B[i]:
            cnt += max(0, B[i] - A[i] + 1)
        else:
            cnt += max(0, m - A[i])
    return cnt < K

N, K = map(int, readline().split())
A, B = [0] * N, [0] * N
for i in range(N):
    A[i], B[i] = map(int, readline().split())

yes = 0
no = 10 ** 10
while no - yes != 1:
    mid = (yes + no)//2
    if check(mid):
        yes = mid
    else:
        no = mid
print(yes)