#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/polygon/point_data.hpp>
#include <boost/polygon/voronoi.hpp>
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(x) begin(x),end(x)
#define sz(x) (int)(x).size()
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
using vll=vector<ll>;
using vvll=vector<vll>;
using vi=vector<int>;
using vvi=vector<vi>;
using pll=pair<ll,ll>;
using pi=pair<int,int>;

using mint=modint998244353;
// using mint=modint1000000007;
// using mint2=static_modint<2>;

// using BoostPoint=boost::polygon::point_data<int>;
// using Voronoi=boost::polygon::voronoi_diagram<double>;

int main()
{
  	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N;
	string S;
	cin>>N>>S;
	vi cnt(26);
	for(auto s:S)cnt[s-'a']++;
	auto ok=[N](int k,vi cnt){
		string target="yuki";
		int alive=k,alive2=N;
		for(auto c:target){
			rrep(i,c-'a'+1,26){
				int mn=min(alive,cnt[i]);
				alive2-=mn;
				alive-=mn;
				cnt[i]-=mn;
			}
			if(alive>cnt[c-'a'])return false;
			cnt[c-'a']-=alive;
			alive2-=alive;
		}
		if(alive>alive2)return false;
		else return true;
	};
	int lo=0,hi=N+1;
	while(hi-lo>1){
		int mid=(lo+hi)/2;
		if(ok(mid,cnt))lo=mid;
		else hi=mid;
	}
	cout<<lo<<'\n';
}