from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue,copy,time
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inp(): return int(sys.stdin.readline())
def inpl(): return list(map(int, sys.stdin.readline().split()))
def inpl_str(): return list(sys.stdin.readline().split())

N = inp()
sA = sB = 0
AA = []
BB = []
for i in range(N-1):
    A,B = inpl()
    AA.append(A)
    BB.append(B)
    sA += A
    sB += B

if N == 2:
    print(1)
else:
    minA = minB = 0
    for i in range(N-1):
        A,B = AA[i],BB[i]
        minB = max(minB, A - (sB-B))
        minA = max(minA, B - (sA-A))

    maxA = sB
    maxB = sA

    ans = min(maxA - minA , maxB - minB) + 1
    print(ans)