N = gets.to_i
Q = (N - 1).times.map { gets.split.map(&:to_i) }

in_cnt = 0
out_cnt = 0

Q.each do |a, b|
  in_cnt += a
  out_cnt += b
end

ans = 0

0.upto(4_000_000) do |a|
  b = (a + in_cnt) - out_cnt
  next if b < 0
  ans += 1
end

puts ans