N = gets.chomp.to_i
b = Array.new(N)
str = gets.split
for i in 0...N-1 do
    b[i] = str[i].to_i
end

answer = b[0] + b[N-2]
for i in 0...N-2 do
    answer += b[i] < b[i+1] ? b[i] : b[i+1]
end

puts answer