#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']});
    }
    */

    ans+=min({mp[0]['c'],mp[1]['o'],mp[2]['n']});

    {
        if(S[0]=='o'){
            mp[0]['o']--;
        }
        if(S[1]=='n'){
            mp[1]['n']--;
        }
        if(S[3*N-1]=='c'){
            mp[2]['c']--;
        }

        ans+=min({mp[2]['c'],mp[0]['o'],mp[1]['n']});


        if(S[0]=='o'){
            mp[0]['o']++;
        }
        if(S[1]=='n'){
            mp[1]['n']++;
        }
        if(S[3*N-1]=='c'){
            mp[2]['c']++;
        }


    }


    {
        if(S[0]=='n'){
            mp[0]['n']--;
        }
        if(S[3*N-2]=='c'){
            mp[1]['c']--;
        }
        if(S[3*N-1]=='o'){
            mp[2]['o']--;
        }

        ans+=min({mp[1]['c'],mp[2]['o'],mp[0]['n']});


       if(S[0]=='n'){
            mp[0]['n']++;
        }
        if(S[3*N-2]=='c'){
            mp[1]['c']++;
        }
        if(S[3*N-1]=='o'){
            mp[2]['o']++;
        }

    }



    cout<<ans<<endl;


}