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

def func(x,AB):
  s = 0
  for a,b in AB:
    if x < a:
      continue
    if x > b:
      s += b-a+1
    elif a <= x <= b:
      s += x-a+1
  return s

r = 10**9+1
l = 0
while r-l > 1:
  mid = (r+l)//2
  s = func(mid,AB)
  if s >= K:
    r  = mid
  elif s < K:
    l = mid
print(r)