n = gets.chomp.to_i
a =[]
b =[]
sum0=sum1=min0=min1=0

(0..(n-2)).each do |i|
 a[i], b[i] = gets.chomp.split(" ").map!(&:to_i)
end

max1=sum0=a.sum
max0=sum1=b.sum

def max(a,b)
 if a > b
   return a
 elsif b > a
   return b
 else
   return a
 end
end

def min(a,b)
 if a > b
   return b
 elsif b > a
   return a
 else
   return a
 end
end

a.each do |x|
 b.each do |y|
   min1 = max(min1, x-(sum1-y))
   min0 = max(min0, y-(sum0-x))
 end
end

p (min((max0-min0+1),(max1-min1+1)))