from heapq import *

n = int(input())
L = [0] * n
R = [0] * n
for i in range(n):
    L[i], R[i] = map(int, input().split())


R_ = sorted(R)
ma = min(r - i for i, r in enumerate(R_))
L_ = sorted(L)
mi = max(l - i for i, l in enumerate(L_))


def ok(x):
    for i in range(n):
        L[i] -= x
        R[i] -= x
        L[i] = max(L[i], 0)
        R[i] = min(R[i], n - 1)

    add = [[] for _ in range(n)]
    for l, r in zip(L, R):
        add[l].append(r)

    hq = []
    for i in range(n):
        for x in add[i]:
            heappush(hq, x)
        while hq and hq[0] < i:
            heappop(hq)
        if not hq:
            return False

        heappop(hq)
    return True


if mi <= ma and ok(ma):
    print(ma - mi + 1)
else:
    print(0)