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

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();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var s = ReadLine();
        var list = new List<char>();
        var one = 0;
        var ans = 0;
        foreach (var c in s)
        {
            if (c == '3' || c == '5' || c == '7') ++ans;
            else list.Add(c);
            if (list.Count > 1 && list[^2] == '1' && list[^1] == '9')
            {
                ++ans;
                list.RemoveAt(list.Count - 1);
                list.RemoveAt(list.Count - 1);
            }
        }
        var nlist = new List<char>();
        foreach (var c in list)
        {
            nlist.Add(c);
            if (nlist.Count > 2 && nlist[^3] == '9' && nlist[^2] == '9' && nlist[^1] == '1')
            {
                ++ans;
                nlist.RemoveAt(nlist.Count - 1);
                nlist.RemoveAt(nlist.Count - 1);
                nlist.RemoveAt(nlist.Count - 1);
            }
        }
        foreach (var c in nlist) if (c == '1') ++one;
        WriteLine(ans + one / 2);
    }
}