n = io.read()
item = {}
pup = 0
for i= 1, n do
  for c in string.gmatch(io.read(),"%d+") do
    if item[c-0] then
      pup = pup + 1
      item[c-0] = nil
    else
      item[c-0] = 1
    end
  end
end

rest = 0
for k, v in pairs(item) do
  rest = rest + (v or 0)
end

pup = pup + math.floor(rest / 4)
print(pup)