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

n = gets.to_i
b = gets.split("\s").map(&:to_i)

result = b[0] + b[n-2]

(n-2).times do |i|
  result += min(b[i], b[i+1])
end

puts result