N = int(input())
AB = [list(map(int, input().split())) for i in range(N-1)]

sa = sum(a for a, _ in AB)
sb = sum(b for _, b in AB)

amin, bmin = 0, 0
for i in range(N-1):
    a, b = AB[i]
    amin = max(amin, b-(sa-a))
    bmin = max(bmin, a-(sb-b))

d = sa - sb
ans = min(sb, sa -d) - max(amin, bmin-d) + 1

print(ans)