N,K = map(int, input().split())

def f(n):
    res = 0
    for t in L:
        if t[0] <= n <= t[1]:
            res += n-t[0]+1
        elif t[1] < n:
            res += t[1]-t[0]+1
    return res

L = [[int(l) for l in input().split()] for _ in range(N)]
l = 1
r = 10**9
while r-l > 1:
    m = (l+r)//2
    if f(m) < K:
        l = m
    else:
        r = m

print(r)