def lscan; gets.split.map(&:to_i); end

la = '0'
total = 0
tw = false
dc = false
gets.chomp.reverse.chars.each do |c|
    if c == '0'
        total += tw ? (dc ? 1 : 2) : 1 if la == '1'
        dc = false if la == '0'
        dc = true  if la == '1'
        la = '0'
    elsif c == '1'
        tw = la == '1'
        la = '1'
    end
end
total += tw ? (dc ? 1 : 2) : 1

p total