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

pup = 0
rest = 0
for k, v in pairs(item) do
  rest = rest + (v % 2)
  pup = pup + math.floor(v / 2) 
end

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