n = int(input())
a_tot = 0
b_tot = 0
max_ = 0
for _ in range(n - 1):
    a, b = map(int, input().split())
    a_tot += a
    b_tot += b
    max_ = max(max_, a + b)

max_a = b_tot
min_a = max(0, max_ - a_tot)
a = max_a - min_a + 1

max_b = a_tot
min_b = max(0, max_ - b_tot)
b = max_b - min_b + 1
print(min(a, b))