N = gets.to_i
P = gets.split.map(&:to_i)
idx = P.index(N) + 1
rounds = Hash.new

P.each.with_index(1) do |x, i|
  rounds[x] = i
end

i = N
sum = (1..N).sum

while i >= 2 && 2 * rounds[i - 1] <= rounds[i]
  sum -= rounds[i]
  i -= 1
end

puts [0, sum - 2 * rounds[i]].max