using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var two = 0L;
        var four = 0L;
        var ans = 0L;
        for (var i = 0; i < n; ++i)
        {
            var c = NList;
            if (c[0] % 8 == 0) ans += c[1];
            else if (c[0] % 4 == 0) four += c[1];
            else if (c[0] % 2 == 0) two += c[1];
        }
        var tf = Math.Min(two, four);
        two -= tf;
        four -= tf;
        WriteLine(ans + tf + two / 3 + four / 2);
    }
}