#include <bits/stdc++.h>

#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 reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define repp(i, n) rep(i, n)
#define reppp(i, n) repp(i, n)
#define rrepp(i, n) rrep(i, n)
#define repss(i, n) reps(i, n)
#define repcc(i, n) repc(i, n)
#define repii(i, a, b) repi(i, a, b)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit(b) (1ll << (b))

using namespace std;

using i32 = int;
using i64 = long long;
using u64 = unsigned long long;
using f80 = long double;
using vi32 = vector<i32>;
using vi64 = vector<i64>;
using vu64 = vector<u64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() { cout << "Yes" << '\n'; exit(0); }
inline void no() { cout << "No" << '\n'; exit(0); }
inline i64 gcd(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); if (a % b == 0) return b; return gcd(b, a % b); }
inline i64 lcm(i64 a, i64 b) { return a / gcd(a, b) * b; }
inline u64 xorshift() { static u64 x = 88172645463325252ull; x = x ^ (x << 7); return x = x ^ (x >> 9); }
void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(16); solve(); return 0; }
template <typename T> class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T> class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { if (x < y) x = y; }
template <typename T> inline void amin(T &x, T y) { if (x > y) x = y; }
template <typename T> inline T power(T x, i64 n, T e = 1) { T r = e; while (n > 0) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; }
template <typename T> istream& operator>>(istream &is, vector<T> &v) { each(x, v) is >> x; return is; }
template <typename T> ostream& operator<<(ostream &os, vector<T> &v) { rep(i, v.size()) { if (i) os << ' '; os << v[i]; } return os; }
template <typename T, typename S> istream& operator>>(istream &is, pair<T, S> &p) { is >> p.first >> p.second; return is; }
template <typename T, typename S> ostream& operator<<(ostream &os, pair<T, S> &p) { os << p.first << ' ' << p.second; return os; }

void solve() {
  int N; cin >> N;
  vstr s(N);
  rep(i, N) cin >> s[i];

  auto b = vector<vector<bool>>(N, vector<bool>(N));
  function<int(int)> rec = [&](int n) {
    if (n == N) {
      int ans = 0;
      unordered_set<int> se;
      rep(i, N) {
        int cnt = 0;
        rep(j, N) if (i != j && b[i][j]) cnt++;
        if (i == 0) ans = cnt;
        if (i > 0 && ans < cnt) se.insert(cnt);
      }
      return 1 + (int) se.size();
    }
    int mn = 1e9;
    rep(i, bit(n)) {
      bool f = true;
      rep(j, n) {
        b[n][j] = (i & bit(j)) != 0;
        b[j][n] = !b[n][j];
        if (s[n][j] == 'o' && !b[n][j]) { f = false; break; }
        if (s[n][j] == 'x' && b[n][j]) { f = false; break; }
      }
      if (f) amin(mn, rec(n + 1));
    }
    return mn;
  };
  cout << rec(0) << '\n';

}