///////////////////////////// No.29 パワーアップ
    //入力文字読み取り
    var inputall = require('fs').readFileSync('/dev/stdin', 'utf8');

    //すべて受け取り改行で区切って格納
    var input = inputall.split("\n");

    var num = Number(input[0]);


    var count = [0,0,0,0,0,0,0,0,0,0,0];
    for (var i = 1; i <= num; i++) {
        var nama = [];
        nama = input[i].split(" ").map(Number);
        for (var j = 0; j < nama.length; j++) {
            if (nama[j] == 0) {
                count[0] ++;
            } else if (nama[j] == 1) {
                count[1] ++;
            } else if (nama[j]== 2) {
                count[2] ++
            } else if (nama[j] == 3) {
                count[3]++
            } else if (nama[j] == 4) {
                count[4]++
            } else if (nama[j]== 5) {
                count[5]++
            } else if (nama[j] == 6) {
                count[6]++
            } else if (nama[j] == 7) {
                count[7]++
            } else if (nama[j] == 8) {
                count[8]++
            } else if (nama[j] == 9) {
                count[9]++
            } else if (nama[j] == 10) {
                count[10]++
            }
            }
    }

    var result = 0;
    var remainder = 0;
    for (var i = 1; i < count.length; i++) {
        result += Math.floor(count[i] / 2);
        remainder +=  count[i] % 2
    }

    if (remainder >= 8) {
        console.log(result+2)
    } else if (remainder >= 4 && remainder < 8) {
        console.log(result + 1)
    } else {
        console.log(result)
    }