n = gets.chomp.to_i
b = gets.chomp.split(' ').map(&:to_i)
a = 0

if n == 2 then
    a += b[0] * 2
else
    a += b[0]
    for i in 0..n-3 do
        if b[i] < b[i+1] then
            a += b[i]
        else
            a += b[i+1]
        end
    end
    a += b[n-2]
end

puts a