#include<iostream>
using namespace std;
int N;
string s;
int cnt[128];
main()
{
	cin>>N>>s;
	for(int i=0;i<N;i++)cnt[s[i]]++;
	int now=0;
	for(char c='a';c<'i';c++)now+=cnt[c];
	if(cnt['i']<=now)now=cnt['i'];
	else now=(now+cnt['i'])/2;
	for(char c='i'+1;c<'k';c++)now+=cnt[c];
	if(cnt['k']<=now)now=cnt['k'];
	else now=(now+cnt['k'])/2;
	for(char c='k'+1;c<'u';c++)now+=cnt[c];
	if(cnt['u']<=now)now=cnt['u'];
	else now=(now+cnt['u'])/2;
	for(char c='u'+1;c<'y';c++)now+=cnt[c];
	if(cnt['y']<=now)now=cnt['y'];
	else now=(now+cnt['y'])/2;
	cout<<now+cnt['z']<<endl;
}