# -*- coding: utf-8 -*-

def main
  n = gets.chop.to_i
  bs = gets.chop.split.map(&:to_i)
  ans = 0
  if n == 2
    puts (bs[0] * 2)
   else
     ans += bs[0]
     0.upto(n - 3) do |i|
       b1 = bs[i]
       b2 = bs[i+1]
       ans += [b1, b2].min
     end
     ans += bs[n-2]
     puts ans
  end
end

if __FILE__ == $0
  main
end

