#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i < (int)(n+1); i++)
#define repn(i,a,b) for (int i = (int)(a) ; i < (int)(b+1); i++)
#define repv(i, n) for (int i = (int)(n-1); i >= 0; i--)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define sz(x) ((int)(x).size())
#define cauto const auto&
#define bit(n) (1LL<<(n))
#define uni(v) v.erase( unique(v.begin(), v.end()), v.end() );
using ll = long long;
using P = pair<int,int>;
using PP = pair<int, P>;
using Graph = vector<vector<int>>;
using mint = modint998244353;
#ifdef LOCAL
    #include <debug.hpp>
    #define debug(...) debug::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
    #define debug(...) (static_cast<void>(0))
#endif

int main(){
    int n;
    cin >> n;
    string s;
    cin >> s;
    int c_1 = 0, c_2 = 0, c_3 = 0, o_1 = 0, o_2 = 0, o_3 = 0, n_1 = 0, n_2 = 0, n_3 = 0;
    rep(i,sz(s)){
        if(i%3==0){
            if(s[i]=='c') c_1++;
            else if(s[i]=='o') o_1++;
            else if(s[i]=='n') n_1++;
        }
        else if(i%3==1){
            if(s[i]=='c') c_2++;
            else if(s[i]=='o') o_2++;
            else if(s[i]=='n') n_2++;
        }
        else{
            if(s[i]=='c') c_3++;
            else if(s[i]=='o') o_3++;
            else if(s[i]=='n') n_3++;
        }
    }
    debug(c_1, c_2, c_3);
    debug(o_1, o_2, o_3);
    debug(n_1, n_2, n_3);
    int ans1 = 1e9;
    ans1 = min(ans1, c_1);
    ans1 = min(ans1, o_2);
    ans1 = min(ans1, n_3);
    int ans2 = 1e9;
    ans2 = min(ans2, c_2);
    ans2 = min(ans2, o_3);
    ans2 = min(ans2, n_1);
    int ans3 = 1e9;
    ans3 = min(ans3, c_3);
    ans3 = min(ans3, o_1);
    ans3 = min(ans3, n_2);
    ans1 = min(ans1, n);
    ans2 = min(ans2, n-ans1);
    ans3 = min(ans3, n-ans1-ans2);
    int ans = 0;
    ans += ans1;
    ans += ans2;
    ans += ans3;
    cout << ans << endl;
    return 0;
}