using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
static class Program{
	const int mod=(int)1e9+7;
	const double eps=1e-11;
	static void Main(){
		Sc sc=new Sc();
		var n=sc.I;
		var t=sc.S;
		var h=new int['z'+1];
		int ans=0;
		for(int i = 0;i<n;i++) {
			h[t[i]]++;
		}
		ans+=h['z'];
		int a=0;
		for(int i = 'v';i<'y';i++) {a+=h[i];}
		a=Min(a,h['y']);
		ans+=a;
		h['y']-=a;
		a=0;
		for(int i = 'l';i<'u';i++) {a+=h[i];}
		a=Min(a,Min(h['y'],h['u']));
		ans+=a;
		h['y']-=a;
		h['u']-=a;
		a=h['j'];
		a=Min(a,Min(h['y'],Min(h['u'],h['k'])));
		ans+=a;
		h['y']-=a;
		h['u']-=a;
		h['k']-=a;
		a=0;
		for(int i = 'a';i<'i';i++) {a+=h[i];}
		a=Min(a,Min(h['y'],Min(h['u'],Min(h['k'],h['i']))));
		ans+=a;
		h['y']-=a;
		h['u']-=a;
		h['k']-=a;
		h['i']-=a;
		a=Min(h['y'],Min(h['u'],Min(h['k'],h['i'])));
		if(a>0&&h['i']/2>0){
			a=Min(h['i']/2,a);
			h['y']-=a;
			h['u']-=a;
			h['k']-=a;
			ans+=a;
		}
		a=Min(h['y'],Min(h['u'],h['k']));
		if(a>0&&h['k']/2>0){
			a=Min(h['k']/2,a);
			h['y']-=a;
			h['u']-=a;
			ans+=a;
		}
		a=Min(h['y'],h['u']);
		if(a>0&&h['u']/2>0){
			a=Min(h['u']/2,a);
			h['y']-=a;
			ans+=a;
		}
		ans+=h['y']/2;
		Console.WriteLine(ans);
	}
}

public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),int.Parse);}
	public int[] Ia3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),long.Parse);}
	public long[] La3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),long.Parse);}
	public double[] Da2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),double.Parse);}}
	public double[] Da3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),double.Parse);}
	public double[] Da3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),double.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}