import sys
readline=sys.stdin.readline

def Bisect_Int(ok,ng,is_ok):
    while abs(ok-ng)>1:
        mid=(ok+ng)//2
        if is_ok(mid):
            ok=mid
        else:
            ng=mid
    return ok

N,K=map(int,readline().split())
A,B=[],[]
for _ in range(N):
    a,b=map(int,readline().split())
    b+=1
    A.append(a)
    B.append(b)
def is_ok(ans):
    cnt=0
    for a,b in zip(A,B):
        cnt+=max(0,min(b,ans)-a)
    return cnt<K
ans=Bisect_Int(0,1<<30,is_ok)
print(ans)