#include <bits/stdc++.h>
using namespace std;
int backet[26];
int main(){
	int n;	cin>>n;
	string s;	cin>>s;
	for(int i=0;i<n;i++)	backet[s[i]-'a']++;
	int yuki[]={24,20,10,8};
	int ans=backet[25];
	int use=backet[24];
	for(int i=1;i<4;i++){
		for(int j=yuki[i-1]-1;j>yuki[i];j--){
			ans+=min(backet[j],use);
			use-=min(backet[j],use);
			if(use<=0)	goto end;
		}
		if(yuki[i]-use<0){
			int cnt=use-yuki[i];
			ans+=cnt/2;
			use-=(cnt/2)*2;
			if(cnt%2&&use)	ans++,use--;
		}
		else if(yuki[i]-use>0){
			int cnt=yuki[i]-use;
			ans+=min(use,cnt);
			use-=min(use,cnt);
		}
	}
	for(int i=7;i>=0;i--){
		ans+=min(use,backet[i]);
		use-=min(use,backet[i]);
	}
	end:;
	cout<<ans<<endl;
	return 0;
}