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

#ifdef _RUTHEN
#include <debug.hpp>
#else
#define show(...) true
#endif

using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
template <class T> using V = vector<T>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N;
    cin >> N;
    string S;
    cin >> S;
    V<V<int>> cnt(3, V<int>(26));
    rep(i, 3 * N) cnt[i % 3][S[i] - 'a']++;
    int ans = 0;
    rep(i, 3) ans += min({cnt[(i + 0) % 3]['c' - 'a'], cnt[(i + 1) % 3]['o' - 'a'], cnt[(i + 2) % 3]['n' - 'a']});
    cout << ans << '\n';
    return 0;
}