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

min_k = get_min_k()
if min_k is None:
    print(0)
else:
    max_k = min(r - (i + 1) for i, r in enumerate(sorted(r for _, r in lr)))
    print(max_k - min_k + 1)