#yuki817

n,k=map(int,raw_input().split())
ab=[]
for i in xrange(n):
 ab.append(map(int,raw_input().split()))
l=0
r=10**9
while r-l>1:
 mid=(l+r)/2
 cnt=0
 for a,b in ab:
  if a>mid:
   continue
  cnt+=min(b,mid)-a+1
 if cnt>=k:
  r=mid
 else:
  l=mid
print r