open System
type Sol() =
    member this.Solve() = 
        let N = stdin.ReadLine() |> int
        let sum = Array.zeroCreate<int> 11
        for i = 0 to (N-1) do
            let a = stdin.ReadLine().Split() |> Array.map int
            a |> Array.iter (fun x -> (sum.[x] <- sum.[x] + 1) )
        
        let powerUp2 = (Array.sumBy (fun e -> e/2 ) sum )
        let powerUp4 = (Array.sumBy (fun e -> e%2 ) sum ) / 4
        
        (powerUp2 + powerUp4) |> printfn "%d"
        
let mySol = new Sol()
mySol.Solve()