#include <bits/stdc++.h>
using namespace std;

int main() {
    int64_t N;
    string S;
    cin >> N >> S;
    vector<int64_t> c_num(3, 0), o_num(3, 0), n_num(3, 0);
    for (int64_t i = 0; i < 3 * N; i++) {
        if (S[i] == 'c') {
            c_num[i % 3]++;
        } else if (S[i] == 'o') {
            o_num[i % 3]++;
        } else if (S[i] == 'n') {
            n_num[i % 3]++;
        }
    }

    int64_t ans = 0;
    ans += min({ c_num[0], o_num[1], n_num[2] });
    ans += min({ c_num[1], o_num[2], n_num[0] });
    ans += min({ c_num[2], o_num[0], n_num[1] });

    cout << ans << endl;
}