N, K = map(int, input().split())
m = []
for i in range(N):
    A, B = map(int, input().split())
    m.append([1, A])
    m.append([-1, B+1])
m.sort(key = lambda x:x[1])
id, cnt, all_num = 0, 0, 0
s = m[0][1]
while True:
    w, n = m[id]
    if s == n:
        cnt += w
        id += 1
    else:
        if all_num + cnt * (n-s) < K:
            all_num += cnt*(n-s)
            s = n
        else:
            c, d = divmod((K-all_num), cnt)
            print(s+(c-1)+(d>0))
            break