from sys import stdin
input = stdin.readline
from heapq import heappush, heappop

def func(k):
    idx = 0
    que = []
    for i in range(1, N+1):
        n = i+k
        while idx < N and LR[idx][0] <= n:
            heappush(que, LR[idx][1])
            idx += 1
        if not que: return -1
        if que[0] < n: return 1
        heappop(que)
    return 0

N = int(input())
LR = [list(map(int, input().split())) for _ in range(N)]

LR.sort(key=lambda x:x[0])

left = -1
right = 10**9
while left+1 < right:
    mid = (left+right)//2
    if func(mid) == -1:
        left = mid
    else:
        right = mid
L = left+1

left = -1
right = 10**9
while left+1 < right:
    mid = (left+right)//2
    if func(mid) == 1:
        right = mid
    else:
        left = mid
R = right-1

print(R-L+1)