#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
#define rep(i, a, b) for(ll i = a; i < b; ++i)
#define rrep(i, a, b) for(ll i = a; i >= b; --i)
constexpr ll inf = 4e18;
struct SetupIO {
    SetupIO() {
        ios::sync_with_stdio(0);
        cin.tie(0);
        cout << fixed << setprecision(30);
    }
} setup_io;
int main(void) {
    int N;
    string S;
    cin >> N >> S;
    vector<vector<int>> cnt(3, vector<int>(3, 0));
    rep(i, 0, N) {
        rep(j, 0, 3) {
            if(S[3 * i + j] == 'c') cnt[0][j]++;
            if(S[3 * i + j] == 'o') cnt[1][j]++;
            if(S[3 * i + j] == 'n') cnt[2][j]++;
        }
    }
    if(min({cnt[0][0], cnt[1][1], cnt[2][2]}) == N) {
        cout << N << '\n';
        return 0;
    }
    int ans = min(min({cnt[0][0], cnt[1][1], cnt[2][2]}) + min({cnt[0][1], cnt[1][2], cnt[2][0]}) + min({cnt[0][2], cnt[1][0], cnt[2][1]}), N - 1);
    cout << ans << '\n';
}