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
    for _ in range(n - 1):
        a,b = map(int,input().split())
        tota += a
        totb += b
    ans = totb - max(totb - tota,0) + 1
    print(ans)

if __name__ =='__main__':
    main()