#pragma region Macros

// #pragma GCC target("avx,avx2,fma")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

#include <bits/extc++.h>
// #include <bits/stdc++.h>
using namespace std;
using namespace __gnu_pbds;
// using namespace __gnu_cxx;
// #include <atcoder/fenwicktree>
// #include <atcoder/segtree>
// #include <atcoder/maxflow>
// using namespace atcoder;

// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// using Bint = mp::cpp_int;

#define TO_STRING(var) # var
#define pb emplace_back
#define int ll
#define endl '\n'

using ll = long long;
using ld = long double;
const ld PI = acos(-1);
const ld EPS = 1e-10;
const ll INFL = 1LL << 61;
const int MOD = 998244353;
// const int MOD = 1000000007;

__attribute__((constructor))
void constructor() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
}

template<int mod> class modint{
public:
    int val = 0;
    modint(int x = 0) { while (x < 0) x += mod; val = x % mod; }
    modint(const modint &r) { val = r.val; } // コピーコンストラクタ

    modint operator -(){ return modint(-val); } // 単項
    modint operator +(const modint &r) { return modint(*this) += r; }
    modint operator -(const modint &r) { return modint(*this) -= r; }
    modint operator *(const modint &r) { return modint(*this) *= r; }
    modint operator /(const modint &r) { return modint(*this) /= r; }

    modint &operator +=(const modint &r) {
        val += r.val;
        if (val >= mod) val -= mod;
        return *this;
    }
    modint &operator -=(const modint &r) {
        if (val < r.val) val += mod;
        val -= r.val;
        return *this;
    }
    modint &operator *=(const modint &r) {
        val = val * r.val % mod;
        return *this;
    }
    modint &operator /=(const modint &r) {
        int a = r.val, b = mod, u = 1, v = 0;
        while (b) {
            int t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % mod;
        if (val < 0) val += mod;
        return *this;
    }

    bool operator ==(const modint& r) { return this -> val == r.val; }
    bool operator <(const modint& r) { return this -> val < r.val; }
    bool operator !=(const modint& r) { return this -> val != r.val; }
};

using mint = modint<MOD>;

istream &operator >>(istream &is, mint& x) {
    int t; is >> t;
    x = t;
    return (is);
}
ostream &operator <<(ostream &os, const mint& x) {
    return os << x.val;
}

mint modpow(const mint &a, int n) {
    if (n == 0) return 1;
    mint t = modpow(a, n / 2);
    t = t * t;
    if (n & 1) t = t * a;
    return t;
}

int modpow(int x, int N, int mod) {
    int ret = 1;
    while (N > 0) {
        if (N % 2 == 1) ret = ret * x % mod;
        x = x * x % mod;
        N /= 2;
    }
    return ret;
}

int ceil(int x, int y) { return (x > 0 ? (x + y - 1) / y : x / y); }

#pragma endregion

signed main() {
    int N;
    string S;
    cin >> N >> S;

    int cnt0c = 0, cnt0o = 0, cnt0n = 0;
    int cnt1c = 0, cnt1o = 0, cnt1n = 0;
    int cnt2c = 0, cnt2o = 0, cnt2n = 0;
    for (int i = 0; i < 3 * N; i++) {
        if (i % 3 == 0 && S[i] == 'c') cnt0c++;
        if (i % 3 == 0 && S[i] == 'o') cnt0o++;
        if (i % 3 == 0 && S[i] == 'n') cnt0n++;

        if (i % 3 == 1 && S[i] == 'c') cnt1c++;
        if (i % 3 == 1 && S[i] == 'o') cnt1o++;
        if (i % 3 == 1 && S[i] == 'n') cnt1n++;

        if (i % 3 == 2 && S[i] == 'c') cnt2c++;
        if (i % 3 == 2 && S[i] == 'o') cnt2o++;
        if (i % 3 == 2 && S[i] == 'n') cnt2n++;
    }
    // cout << cnt0c << " " << cnt1o << " " << cnt2n << " " << cnt0o << " " << cnt1n << " " << cnt2c << " " << cnt0n << " " << cnt1c << " " << cnt2o << endl;

    int ans = min({cnt0c, cnt1o, cnt2n}) + min({cnt0n, cnt1c, cnt2o}) + min({cnt0o, cnt1n, cnt2c});
    // int ans2 = min({cnt0c, cnt1n, cnt2o}) + min({cnt0o, cnt1c, cnt2n}) + min({cnt0n, cnt1o, cnt2c});
    cout << ans << endl;
}