MOD = 10 ** 9 + 7
INF = 10 ** 10
import sys
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)
from collections import deque
from heapq import heapify,heappush,heappop

def main():
    n = int(input())
    tota = 0
    totb = 0
    M = 0
    for _ in range(n - 1):
        a,b = map(int,input().split())
        tota += a
        totb += b
        M = max(M,a + b)
    
    ans = 0
    for i in range(totb + 1):
        j = i + tota - totb
        if j < 0 or j < M - totb:
            continue
        ans += 1
    
    print(ans)

if __name__ =='__main__':
    main()