N=int(input())
A,B=[],[]
for i in range(N-1):
    a,b=map(int,input().split())
    A.append(a)
    B.append(b)
def check(A,B):
    sum_A=sum(A)
    sum_B=sum(B)
    return sum_A==sum_B and all(a+b<=sum_A for a,b in zip(A,B))
sum_A=sum(A)
sum_B=sum(B)
ans=0
for a in range(4*10**5):
    b=sum_A+a-sum_B
    if 0<=b and check(A+[a],B+[b]):
        ans+=1
print(ans)