import heapq

n = int(input())
lr = [tuple(map(int, input().split())) for _ in range(n)]

def check(k: int):
    pq = []
    j = 0
    for v in range(k + 1, k + n + 1):
        while j < n and lr[j][0] <= v:
            heapq.heappush(pq, lr[j][1])
            j += 1
        if pq[0] < v:
            return False
        heapq.heappop(pq)
    return True


def get_min_k():
    lr.sort(key=lambda t: t[0])
    k = max(lr[i][0] - (i + 1) for i in range(n))
    return k if check(k) else None

min_k = get_min_k()
if min_k is None:
    print(0)
else:
    ok, ng = min_k, 10 ** 9
    while ng - ok > 1:
        k = (ok + ng) >> 1
        if check(k):
            ok = k
        else:
            ng = k
    print(ok - min_k + 1)