import heapq

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

def get_min_k():
    lr.sort(key=lambda t: t[0])
    k = max(lr[i][0] - (i + 1) for i in range(n))

    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 None
        heapq.heappop(pq)
    return k

M = 10 ** 9 + 1

min_k = get_min_k()
if min_k is None:
    print(0)
else:
    lr = [(M - r, M - l) for l, r in lr]
    max_k = get_min_k()
    assert max_k is not None
    max_k = M - max_k - (n + 1)
    print(max_k - min_k + 1)