def action_handler(n, b_array)
  result = []
  for i in 0..n - 1
    if i == 0
      result.push(b_array[i])
    elsif i == n - 1
      result.push(b_array[i - 1])
    else
      result.push([b_array[i], b_array[i - 1]].min)
    end
  end
  return result.inject(:+)
end

n = gets.to_i
b_array = gets.chop.split.map(&:to_i)

print action_handler(n, b_array)