local n = io.read("*n", "*l")
local s = io.read()
local ret = 0
local cur9 = 0
local cur1 = 0
for i = 1, n do
  local ss = s:sub(i, i):byte() - 48
  if ss == 1 then
    cur1 = cur1 + 1
  elseif ss == 9 then
    if 1 <= cur1 then
      -- 19
      cur1 = cur1 - 1
      ret = ret + 1
    else
      cur9 = cur9 + 1
    end
  else
    ret = ret + 1
  end
end
-- 991
local z = math.min(cur1, math.floor(cur9 / 2))
ret = ret + z
cur1 = cur1 - z
-- 11
ret = ret + math.floor(cur1 / 2)
print(ret)