n = gets.to_i
s = gets.chomp.chars.map(&:to_i)
a = 0
(0...(n - 2)).each do |i|
  next unless s[i] == 0 && s[i + 1] == 1 && s[i + 2] == 0

  a += 1
  s[i + 2] = 1
end
(0...(n - 1)).each do |i|
  next unless s[i] == 0 && s[i + 1] == 0

  a += 1
  s[i + 1] = 1
end
(0...(n - 2)).each do |i|
  next unless s[i] == 0 && s[i + 1] == 1 && s[i + 2] == 0

  a += 1
  s[i + 2] = 1
end

puts a