n,k = map(int,input().split())
x = [list(map(int,input().split())) for i in range(n)]


def  check(a):
    cnt=0
    for i,j in x:
        if i <= a:
            cnt += min(a,j) - i + 1
    if cnt < k:
        return False
    else:
        return True

ng = 0
ok = 10**9

while ok-ng > 1:
    mid = (ok + ng) // 2
    if check(mid):
        ok = mid
    else:
        ng = mid

print(ok)