#include<iostream>
#include<set> 
#include<algorithm>
#include<vector>
#include<string>
#include<set>
#include<map>
#include<numeric>
#include<queue>
#include<cmath>
#include <unordered_set>
using namespace std;
typedef long long ll;
const ll INF=1LL<<60;
typedef pair<ll,ll> P;
typedef pair<int,P> PP;
const ll MOD=1e9+7;


int main(){
    int N;
    cin>>N;
    string S;
    cin>>S;
    vector<map<char,int>> mp(3);

    for(int i=0;i<3*N;i++){
        mp[i%3][S[i]]++;
    }
    int ans=0;
    for(int i=0;i<3;i++){
        //min({mp[0]['c'],mp[1]['o'],mp[2]['n']})
        //ans=max(ans,min({mp[i]['c'],mp[(i+1)%3]['o'],mp[(i+2)%3]['n']}));
        ans+=min({mp[i]['c'],mp[(i+1)%3]['o'],mp[(i+2)%3]['n']});
    }
    cout<<ans<<endl;


}