#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic pop
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  string s;
  cin >> n >> s;
  int cnt[3][3]{};
  rep(i, 3 * n) {
    int p = s[i] == 'c' ? 0 : s[i] == 'o' ? 1 : s[i] == 'n' ? 2 : -1;
    if (p >= 0) cnt[i % 3][p]++;
  }
  int nxt = 0;
  int ans = 0;
  rep(r, 3) {
    while(nxt % 3 != r) nxt++;
    if (nxt >= 3 * n) break;
    int c = min({(3 * n - nxt) / 3, cnt[r][0], cnt[(r+1)%3][1], cnt[(r+2)%3][2]});
    ans += c;
    nxt += 3 * c;
  }
  cout << ans << '\n';
}