N = gets.to_i
A = gets.split.map(&:to_i)
B = []
MAX_L = Array.new(N)
MIN_L = Array.new(N)
MAX_R = Array.new(N)
MIN_R = Array.new(N)

A.each_with_index do |a, i|
  idx = B.bsearch_index { |b| b > a }

  if idx
    MAX_L[i] = B[idx]
  end

  idx ||= B.size

  if idx - 1 >= 0
    MIN_L[i] = B[0]
  end

  B.insert(idx, a)
end

C = []

A.reverse.each.with_index(1) do |a, i|
  idx = C.bsearch_index { |b| b > a }

  if idx
    MAX_R[-i] = C[idx]
  end

  idx ||= C.size

  if idx - 1 >= 0
    MIN_R[-i] = C[0]
  end

  C.insert(idx, a)
end

ans = Float::INFINITY

N.times do |i|
  a = A[i]

  if MAX_L[i] && MAX_R[i]
    v = a + MAX_L[i] + MAX_R[i]
    ans = v if ans > v
  end

  if MIN_L[i] && MIN_R[i]
    v = a + MIN_L[i] + MIN_R[i]
    ans = v if ans > v
  end
end

if ans == Float::INFINITY
  puts -1
else
  puts ans
end