#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<to;x++)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N;
string S;
int num[7];
int ret;
void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>S;
	FOR(i,N) {
		if(S[i]=='z') ret++;
		else if(S[i]=='y') num[0]++;
		else if(S[i]>'u')  num[1]++;
		else if(S[i]=='u') num[2]++;
		else if(S[i]>'k')  num[3]++;
		else if(S[i]=='k') num[4]++;
		else if(S[i]>'i')  num[5]++;
	}
	
	while(num[0]&&num[2]&&num[4]&&num[5]) {
		ret++;
		num[0]--;
		num[2]--;
		num[4]--;
		num[5]--;
	}
	while(num[0]&&num[2]&&num[4]>=2) {
		ret++;
		num[0]--;
		num[2]--;
		num[4]-=2;
	}
	while(num[0]&&num[2]&&num[3]) {
		ret++;
		num[0]--;
		num[2]--;
		num[3]--;
	}
	while(num[0]&&num[2]>=2) {
		ret++;
		num[0]--;
		num[2]-=2;
	}
	while(num[0]&&num[1]) {
		ret++;
		num[0]--;
		num[1]--;
	}
	while(num[0]>=2) {
		ret++;
		num[0]-=2;
	}
	
	
	
	cout<<ret<<endl;
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false);
	FOR(i,argc-1) s+=argv[i+1],s+='\n';
	FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	solve(); return 0;
}