n = int(input())
a_list = []
b_list = []
for _ in range(n - 1):
    a, b = map(int, input().split())
    a_list.append(a)
    b_list.append(b)

sum_a_other = sum(a_list)
sum_b_other = sum(b_list)
s = sum_a_other - sum_b_other

# Calculate lower_a_max
lower_a = []
for a_i, b_i in zip(a_list, b_list):
    term = a_i - (sum_b_other - b_i) - s
    lower_a.append(term)
lower_a_max = max(lower_a) if lower_a else -float('inf')

# Calculate lower_b_max
lower_b = []
for a_i, b_i in zip(a_list, b_list):
    term = b_i - (sum_a_other - a_i)
    lower_b.append(term)
lower_b_max = max(lower_b) if lower_b else -float('inf')

# Calculate max_c
max_c = max(-s, 0)

current_lower = max(lower_a_max, lower_b_max, max_c)
upper = sum_b_other

if current_lower > upper:
    print(0)
else:
    print(upper - current_lower + 1)