#include <bits/stdc++.h>
#pragma warning(disable : 4996)
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("-ffloat-store")
using namespace std;
clock_t time_p = clock();
void aryanc403() {
  time_p = clock() - time_p;
  cerr << "Time Taken : " << (float)(time_p) / CLOCKS_PER_SEC << "\n";
}
const long long int INF = 0xFFFFFFFFFFFFFFFL;
long long int seed;
mt19937 rng(seed = chrono::steady_clock::now().time_since_epoch().count());
inline long long int rnd(long long int l = 0, long long int r = INF) {
  return uniform_int_distribution<long long int>(l, r)(rng);
}
class CMP {
 public:
  bool operator()(pair<long long int, long long int> a,
                  pair<long long int, long long int> b) {
    return !(a.first < b.first || a.first == b.first && a.second <= b.second);
  }
};
void add(map<long long int, long long int> &m, long long int x,
         long long int cnt = 1) {
  auto jt = m.find(x);
  if (jt == m.end())
    m.insert({x, cnt});
  else
    jt->second += cnt;
}
void del(map<long long int, long long int> &m, long long int x,
         long long int cnt = 1) {
  auto jt = m.find(x);
  if (jt->second <= cnt)
    m.erase(jt);
  else
    jt->second -= cnt;
}
bool cmp(const pair<long long int, long long int> &a,
         const pair<long long int, long long int> &b) {
  return a.first < b.first || (a.first == b.first && a.second < b.second);
}
const long long int mod = 1000000007L;
const long long int N = 50L;
long long int T, n, i, j, k, in, cnt, l, r, u, v, x, y;
long long int m;
string s[N + 5];
vector<long long int> a;
long long int dp[N + 5][N + 5][N + 5][N + 5];
long long int solve(long long int lx, long long int ly, long long int rx,
                    long long int ry) {
  long long int &ans = dp[lx][ly][rx][ry];
  if (ans != -1) return ans;
  if (lx == rx && ly == ry) return ans = (s[lx][ly] == '#');
  long long int i;
  ans = INF;
  for (i = (lx); i <= (rx - 1); ++i)
    ans = min(ans, solve(lx, ly, i, ry) + solve(i + 1, ly, rx, ry));
  for (i = (ly); i <= (ry - 1); ++i)
    ans = min(ans, solve(lx, ly, rx, i) + solve(lx, i + 1, rx, ry));
  if (ans) ans = min(ans, 1 + max(ry - ly, rx - lx));
  ;
  return ans;
}
int main(void) {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  {
    cin >> n;
    for (i = 0; i < (n); ++i) cin >> s[i];
    memset(dp, -1,
           (N + 5) * (N + 5) * (N + 5) * (N + 5) * sizeof(long long int));
    cout << solve(0, 0, n - 1, n - 1) << "\n";
  }
  aryanc403();
  return 0;
}
