def bsearch_right(low: int, high: int, pred) -> int:
    assert low <= high
    assert pred(high)
    lo = low
    hi = high
    while lo <= hi:
        m = (lo + hi) // 2
        if pred(m):
            hi = m - 1
        else:
            lo = m + 1

    return hi + 1


# m 円以下が K 枚以上あるか
def can(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_right(1, 10**9, can)
print(ans)