import sys

N=int(input())
S=[tuple(map(int,input().split())) for i in range(N-1)]

SUM0=0
SUM1=0


for x,y in S:
    SUM0+=x
    SUM1+=y

MAX0=SUM1
MAX1=SUM0

MIN0=0
MIN1=0

for x,y in S:
    MIN1=max(MIN1,x-(SUM1-y))
    MIN0=max(MIN0,y-(SUM0-x))

print(min((MAX0-MIN0+1),(MAX1-MIN1+1)))