n = gets.to_i
a = Array.new(n)
b = gets.chomp.split(' ').map(&:to_i)
a[0] = b[0]
a[n - 1] = b[n - 2]
(0..(n - 3)).each do |i|
  a[i + 1] = [b[i], b[i + 1]].min
end
sum = 0
a.each do |i|
  sum += i
end
puts sum