n = int(input())
sum_a = 0
sum_b = 0
for _ in range(n-1):
    a, b = map(int, input().split())
    sum_a += a
    sum_b += b
d = sum_b - sum_a
lower = max(0, sum_a - sum_b)
upper = sum_a
print(upper - lower + 1)