N,K = map(int,input().split())
A = [list(map(int,input().split())) for _ in range(N)]
high = 10**9+1
low = 0
while high-low>1:
    mid = (high+low)//2
    cnt = 0
    for a,b in A:
        if b<mid:
            cnt += (b-a+1)
        elif a<mid<=b:
            cnt += (mid-a)
    if cnt<K:
        low = mid
    else:
        high = mid
print(low)