#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000;
int main(){
  int N;
  cin >> N;
  string S;
  cin >> S;
  string T = "con";
  vector<vector<int>> cnt(3, vector<int>(3, 0));
  for (int i = 0; i < N * 3; i++){
    for (int j = 0; j < 3; j++){
      if (S[i] == T[j]){
        int x = (i - j + 3) % 3;
        cnt[x][j]++;
      }
    }
  }
  int ans = 0;
  for (int i = 0; i < 3; i++){
    int mn = INF;
    for (int j = 0; j < 3; j++){
      mn = min(mn, cnt[i][j]);
    }
    ans += mn;
  }
  cout << ans << endl;
}