n=int(input())
x=[]
c=0;d=0
for i in range(n-1):
    a,b=map(int,input().split())
    c+=b;x.append((a,b));d+=a
a=0;b=0
for i,j in x:
    a=max(a,i+j-c)
    b=max(b,i+j-d)
print(min(d-a+1,c-b+1))