# a + sumA = b + sumB
# a <= sumB, b <= sumA
# b - a = sumA - sumB
# max_{i \in N} (A_i + B_i - sumB) <= b
def max(a,b); a > b ? a : b; end
  
N = gets.to_i
A = Array.new(N - 1,0)
B = Array.new(N - 1,0)

(N-1).times do |i|
  a, b = gets.split.map(&:to_i)
  A[i] = a
  B[i] = b
end
sumA = A.sum
sumB= B.sum

b_min = (N - 1).times.inject(0) do |min,i|
  max(min, A[i] + B[i] - sumB)
end

ans = (b_min .. sumA).count do |b|
  a = b - sumA + sumB
  a >= 0 && a <= sumB 
end
puts ans