var pow:Int = 0
var item:Set = Set<Int>()
let N:Int = Int(readLine()!)!
for _ in 1...N{
    let get = readLine()!.split(separator: " ").map{Int($0)!}
    for i in get{
        if item.contains(i){
            pow += 1
            item.remove(i)
        } else{
            item.insert(i)
        }
    }
}
print(pow + Int(item.count / 4))