using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;



class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        int panelCount = int.Parse(Reader.ReadLine());
        string inpt = Reader.ReadLine();

        char[] big = inpt.Where(a=>a>'y').ToArray();
        char[] nokori = inpt.Where(a=>a<='y').ToArray();
        int ans = this.getAns(nokori) + big.Length;
        Console.WriteLine(ans);
    }

    private int getAns(char[] nokori) {
        int ans = 0;
        char[] y = nokori.Where(a=>a == 'y').ToArray();
        char[] other = nokori.Where(a=>a!='y').ToArray();

        if(other.Count(a=>a > 'u') > 0) {
            char[] uOver = other.Where(a=>a>'u').OrderBy(a=>a).ToArray();
            other = other.Where(a=>a<='u').ToArray();
            if(uOver.Length >= y.Length) {
                return y.Length;
            } else {
                ans = uOver.Length;
                y = y.Skip(uOver.Length).ToArray();
            }
        }
        if(y.Length == 0) {
            return ans;
        }
        if(other.Count(a=>a=='u') > 0) {
            char[] u = other.Where(a=>a=='u').ToArray();
            other = other.Where(a=>a!='u').ToArray();
            if(u.Length > y.Length) {
                u = u.Skip(y.Length).ToArray();
                other = other.Concat(u).ToArray();
            } else if(u.Length < y.Length) {
                other = other.Concat(y.Skip(u.Length)).ToArray();
                y = y.Take(u.Length).ToArray();
            }
        } else {
            y = new char[0];
        }
        if(y.Length == 0) {
            return ans;
        }
        if(other.Count(a=>a>'k') > 0) {
            char[] kOver = other.Where(a=>a>'k').OrderBy(a=>a).ToArray();
            other = other.Where(a=>a <= 'k').ToArray();
            if(kOver.Length >= y.Length) {
                ans += y.Length;
                return ans;
            } else {
                ans += kOver.Length;
                y = y.Skip(kOver.Length).ToArray();
            }
        }
        if(other.Count(a=>a=='k') > 0) {
            char[] k = other.Where(a=>a=='k').ToArray();
            other = other.Where(a=>a!='k').ToArray();

            if(k.Length > y.Length) {
                k = k.Skip(y.Length).ToArray();
                other = other.Concat(k).ToArray();
            } else if(k.Length < y.Length) {
                other = other.Concat(y.Skip(k.Length)).ToArray();
                y = y.Take(k.Length).ToArray();
            }
        } else {
            y = new char[0];
        }
        if(y.Length == 0) {
            return ans;
        }
        if(other.Count(a=>a>'i') > 0) {
            char[] iOver = other.Where(a=>a>'i').OrderBy(a=>a).ToArray();
            other = other.Where(a=>a<='i').ToArray();
            if(iOver.Length < y.Length) {
                ans+=iOver.Length;
                y = y.Skip(iOver.Length).ToArray();
            } else {
                ans+=y.Length;
                return ans;
            }
        }
        if(other.Count(a=>a=='i') > 0) {
            char[] i = other.Where(a=>a=='i').ToArray();
            other = other.Where(a=>a != 'i').ToArray();
            if(i.Length > y.Length) {
                i = i.Skip(y.Length).ToArray();
                other = other.Concat(i).ToArray();
            } else if(i.Length < y.Length) {
                other = other.Concat(y.Skip(i.Length)).ToArray();
                y = y.Take(i.Length).ToArray();
            }
        } else {
            y = new char[0];
        }
        if(y.Length == 0) {
            return ans;
        }
        
        if(other.Length > y.Length) {
            ans += y.Length;
        } else {
            ans += other.Length;
        }
        return ans;
    }




    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"

11
kyuukyuusya


";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}