#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using ld = long double;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    struct con { int c=0, o=0, n=0; };
    int N; string S; cin >> N >> S;
    con x[3];
    rep(i,N)rep(j,3) {
        if(S[i * 3 + j] == 'c') x[j].c++;
        if(S[i * 3 + j] == 'o') x[j].o++;
        if(S[i * 3 + j] == 'n') x[j].n++;
    }

    int ans = 0;
    ans += min({x[0].c, x[1].o, x[2].n});
    ans += min({x[1].c, x[2].o, x[0].n});
    ans += min({x[2].c, x[0].o, x[1].n});
    cout << ans << endl;
}