N = int(input())
ent = [0] * (N - 1)
ext = [0] * (N - 1)
sum_ent = 0
sum_ext = 0
for i in range(N-1):
    ent[i], ext[i] = map(int, input().split())
    sum_ent += ent[i]
    sum_ext += ext[i]
ans = 0
for A in range(sum_ext + 1):
    sum_A = A + sum_ent
    if sum_A - sum_ext >= 0:
        for i in range(N-1):
            if ent[i] > sum_A - ext[i]:
                break
        else:
            ans += 1
print(ans)