#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    int N;
    string S;
    cin>>N>>S;
    vector<map<char,int>> M(3);
    for(int i=0;i<3*N;i++){
        M[i%3][S[i]]++;
    }
    bool p = ((min({M[0]['c'],M[1]['o'],M[2]['n']})>=1)+(min({M[0]['o'],M[1]['n'],M[2]['c'],N-1})>=1)+(min({M[0]['n'],M[1]['c'],M[2]['o'],N-1})>=1)>=2);
    cout<<min(min({M[0]['c'],M[1]['o'],M[2]['n']})+min({M[0]['o'],M[1]['n'],M[2]['c'],N-1})+min({M[0]['n'],M[1]['c'],M[2]['o'],N-1}),N-p)<<endl;
}