from collections import defaultdict
n,k = map(int,input().split())
yen = defaultdict(int)
yen_rot = set()
for i in range(n):
  a,b = map(int,input().split())
  b += 1
  yen_rot.add(a)
  yen_rot.add(b)
  yen[a] += 1
  yen[b] -= 1

yen_rot = list(yen_rot)
yen_rot.sort()

ki = k
prev = -1
pi = 0
for i in yen_rot:
  if pi > 0:
    c = i-prev
    #print(c,ki,pi)
    if c*pi >= ki:
      print(ki//pi+prev)
      break
    else:
      ki -= c*pi
  pi += yen[i]
  prev = i