def reverseNumByArray stdAr
        returnAr = []
        stdAr.each{|num|
                case num
                when '0'
                        returnAr.push('1')
                when '1'
                        returnAr.push('0')
                end
        }
        return returnAr
end


inputN = gets
N = inputN.to_i

inputI = gets
I = inputI.split(' ')

ans = 0
place = 0

for i in 0..(N-1) do
        place = i
        cloneI = I.clone
        while (cloneI[place] != "0") do
                if place == (N - 1) then
                        break
                else
                        place += 1
                        ans += 1
                        cloneI = reverseNumByArray(cloneI)
                end
        end
end

puts ans