let ``No.29 パワーアップ`` () =
    let N = int <| stdin.ReadLine()
    Seq.initInfinite (fun _ -> stdin.ReadLine().Split(' '))
    |> Seq.take N
    |> Seq.collect id
    |> Seq.groupBy id
    |> Seq.map (fun (_,s) -> let n = Seq.length s in n/2,n&&&1)
    |> Seq.fold(fun (s1,s2) (n,a) -> s1+n,s2+a) (0,0)
    |> fun (a,b) -> a + (b/4)
    |> printfn "%A"
``No.29 パワーアップ`` ()