n = int(input())
A = [0]*(n-1)
B = [0]*(n-1)

for i in range(n-1):
    a, b = map(int, input().split())
    A[i], B[i] = a, b

Sa = sum(A)
Sb = sum(B)

ans = 0
for a in range(Sb+1):
    b = a + Sa - Sb
    if b < 0:
        continue
    for i in range(n-1):
        if A[i] > b + Sb - B[i]:
            break
    else:
        ans += 1
print(ans)