#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

int main(){
	
	string temp = "yuki";
	temp += 'a' - 1;
	int N;
	cin>>N;
	string s;
	cin>>s;
	
	vector<int> cnt(26,0);
	rep(i,s.size())cnt[s[i]-'a']++;
	vector<int> c(1,cnt.back());
	
	rep(i,temp.size()-1){
		c.push_back(cnt[temp[i]-'a']);
		c.push_back(0);
		for(int j=temp[i]-'a'-1;j>temp[i+1]-'a';j--){
			c.back() += cnt[j];
		}
	}
	rep(i,c.size()){
		//cout<<c[i]<<endl;
	}
	vector<vector<int>> t = {
		{1,0,0,0,0,0,0,0,0},
			{0,2,0,0,0,0,0,0,0},
				{0,1,1,0,0,0,0,0,0},
					{0,1,0,2,0,0,0,0,0},
						{0,1,0,1,1,0,0,0,0},
							{0,1,0,1,0,2,0,0,0},
								{0,1,0,1,0,1,1,0,0},
									{0,1,0,1,0,1,0,2,0},
										{0,1,0,1,0,1,0,1,1}
	};
	reverse(t.begin(),t.end());
	
	int ans = 0;
	
	rep(i,t.size()){
		while(true){
			bool f = true;
			rep(j,t[i].size()){
				if(t[i][j]<=c[j])continue;
				f = false;
			}
			if(!f)break;
			rep(j,t[i].size()){
				c[j] -= t[i][j];
			}
			ans++;
		}
	}
	
	cout<<ans<<endl;
	
	return 0;
}