def bsearch(low: int, high: int, fun, is_complement=False) -> int:
    def pred(x: int) -> bool:
        return not fun(x) if is_complement else fun(x)

    lo = low
    hi = high
    res = low
    while lo <= hi:
        m = (lo + hi) // 2
        if pred(m):
            res = max(res, m)
            lo = m + 1
        else:
            hi = m - 1

    return res + 1 if is_complement else res


# m 円以下が K 枚以上あるか
def calc(m: int) -> bool:
    res = 0
    for a, b in xs:
        if m < a: continue
        res += min(m, b) - a + 1
        if res >= K:
            return True

    return False


N, K = map(int, input().split())
xs = []
for _ in range(N):
    A, B = map(int, input().split())
    xs.append((A, B))

ans = bsearch(1, 10**9, calc, is_complement=True)
print(ans)