#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s[1000];
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    cin >> s[i];
  }
  char ch = s[0][0];
  int flg = 0, cnc = 0, cnch = 0;
  char c = s[0][1];
  if (c == ch) flg = 1;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (s[i][j] == c) {
        cnc++;
      } else if (s[i][j] == ch) {
        cnch++;
      } else
        flg = 1;
    }
  }
  if (cnch != 2 * n - 1)
    flg = 1;
  else if (n * n - cnch != cnc)
    flg = 1;
  for (int j = 0, i = 0; i < n / 2; i++) {
    if (s[i][i] == s[i][n - i - 1] && ch == s[i][i]) {
    } else
      flg = 1;
  }
  if (s[n / 2][n / 2] != ch) flg = 1;
  for (int j = 0, i = n - 1; i > n / 2; j++, i--) {
    if (s[i][j] == s[i][n - 1 - j] && ch == s[i][j]) {
    } else
      flg = 1;
  }
  if (flg)
    cout << "NO" << endl;
  else
    cout << "YES" << endl;
}
